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 $204.99   4.208%   $213.616   $213.62   $213.60   $213.60  
  Purchase #2 $242.27   8.415%   $262.657   $262.66   $262.65   $262.70  
  Purchase #3 $162.92   9.425%   $178.2752   $178.28   $178.30   $178.30  
  Purchase #4 $118.78   4.443%   $124.0574   $124.06   $124.05   $124.10  
  Purchase #5 $48.35   7.636%   $52.042   $52.04   $52.05   $52.00  
  Purchase #6 $245.29   12.697%   $276.4345   $276.43   $276.45   $276.40  
  Purchase #7 $112.54   5.429%   $118.6498   $118.65   $118.65   $118.60  
  7 purchase totals = $1,135.14       $1,225.7319   $1,225.74   $1,225.75   $1,225.70