Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.43   13.464%   $277.3401   $277.34   $277.35   $277.30  
  Purchase #2 $194.38   13.144%   $219.9293   $219.93   $219.95   $219.90  
  Purchase #3 $139.36   5.457%   $146.9649   $146.96   $146.95   $147.00  
  Purchase #4 $146.59   8.385%   $158.8816   $158.88   $158.90   $158.90  
  Purchase #5 $207.45   8.495%   $225.0729   $225.07   $225.05   $225.10  
  Purchase #6 $106.47   4.152%   $110.8906   $110.89   $110.90   $110.90  
  Purchase #7 $206.65   11.352%   $230.1089   $230.11   $230.10   $230.10  
  7 purchase totals = $1,245.33       $1,369.1883   $1,369.18   $1,369.20   $1,369.20