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 $83.57   11.612%   $93.2741   $93.27   $93.25   $93.30  
  Purchase #2 $72.58   4.687%   $75.9818   $75.98   $76.00   $76.00  
  Purchase #3 $236.77   3.153%   $244.2354   $244.24   $244.25   $244.20  
  Purchase #4 $187.69   6.766%   $200.3891   $200.39   $200.40   $200.40  
  Purchase #5 $164.83   12.503%   $185.4387   $185.44   $185.45   $185.40  
  Purchase #6 $30.82   3.505%   $31.9002   $31.90   $31.90   $31.90  
  Purchase #7 $48.36   11.852%   $54.0916   $54.09   $54.10   $54.10  
  7 purchase totals = $824.62       $885.3109   $885.31   $885.35   $885.30