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 $59.89   3.813%   $62.1736   $62.17   $62.15   $62.20  
  Purchase #2 $186.71   11.326%   $207.8568   $207.86   $207.85   $207.90  
  Purchase #3 $232.74   4.521%   $243.2622   $243.26   $243.25   $243.30  
  Purchase #4 $125.62   10.665%   $139.0174   $139.02   $139.00   $139.00  
  Purchase #5 $22.26   13.612%   $25.29   $25.29   $25.30   $25.30  
  Purchase #6 $215.69   13.345%   $244.4738   $244.47   $244.45   $244.50  
  Purchase #7 $18.44   7.663%   $19.8531   $19.85   $19.85   $19.90  
  7 purchase totals = $861.35       $941.9269   $941.92   $941.85   $942.10