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 $83.63   5.152%   $87.9386   $87.94   $87.95   $87.90  
  Purchase #2 $115.41   10.733%   $127.797   $127.80   $127.80   $127.80  
  Purchase #3 $222.39   9.747%   $244.0664   $244.07   $244.05   $244.10  
  Purchase #4 $18.73   11.712%   $20.9237   $20.92   $20.90   $20.90  
  Purchase #5 $121.26   3.356%   $125.3295   $125.33   $125.35   $125.30  
  Purchase #6 $238.31   12.372%   $267.7937   $267.79   $267.80   $267.80  
  Purchase #7 $47.79   11.123%   $53.1057   $53.11   $53.10   $53.10  
  7 purchase totals = $847.52       $926.9546   $926.96   $926.95   $926.90