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 $58.69   10.332%   $64.7539   $64.75   $64.75   $64.80  
  Purchase #2 $194.36   3.214%   $200.6067   $200.61   $200.60   $200.60  
  Purchase #3 $116.27   7.570%   $125.0716   $125.07   $125.05   $125.10  
  Purchase #4 $90.95   12.468%   $102.2896   $102.29   $102.30   $102.30  
  Purchase #5 $127.65   10.835%   $141.4809   $141.48   $141.50   $141.50  
  Purchase #6 $177.26   4.808%   $185.7827   $185.78   $185.80   $185.80  
  Purchase #7 $108.43   5.445%   $114.334   $114.33   $114.35   $114.30  
  7 purchase totals = $873.61       $934.3194   $934.31   $934.35   $934.40