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 $14.62   11.344%   $16.2785   $16.28   $16.30   $16.30  
  Purchase #2 $134.37   12.551%   $151.2348   $151.23   $151.25   $151.20  
  Purchase #3 $82.68   5.171%   $86.9554   $86.96   $86.95   $87.00  
  Purchase #4 $175.66   5.812%   $185.8694   $185.87   $185.85   $185.90  
  Purchase #5 $31.97   11.372%   $35.6056   $35.61   $35.60   $35.60  
  Purchase #6 $209.29   12.416%   $235.2754   $235.28   $235.30   $235.30  
  Purchase #7 $229.69   6.224%   $243.9859   $243.99   $244.00   $244.00  
  7 purchase totals = $878.28       $955.2050   $955.22   $955.25   $955.30