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 $212.78   13.199%   $240.8648   $240.86   $240.85   $240.90  
  Purchase #2 $204.98   12.664%   $230.9387   $230.94   $230.95   $230.90  
  Purchase #3 $157.77   7.354%   $169.3724   $169.37   $169.35   $169.40  
  Purchase #4 $246.72   4.390%   $257.551   $257.55   $257.55   $257.60  
  Purchase #5 $182.43   7.674%   $196.4297   $196.43   $196.45   $196.40  
  Purchase #6 $248.66   9.809%   $273.0511   $273.05   $273.05   $273.10  
  Purchase #7 $82.85   12.628%   $93.3123   $93.31   $93.30   $93.30  
  7 purchase totals = $1,336.19       $1,461.5200   $1,461.51   $1,461.50   $1,461.60