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 $235.51   12.652%   $265.3067   $265.31   $265.30   $265.30  
  Purchase #2 $117.89   8.112%   $127.4532   $127.45   $127.45   $127.50  
  Purchase #3 $66.77   4.840%   $70.0017   $70.00   $70.00   $70.00  
  Purchase #4 $139.98   3.560%   $144.9633   $144.96   $144.95   $145.00  
  Purchase #5 $209.63   5.340%   $220.8242   $220.82   $220.80   $220.80  
  Purchase #6 $113.59   5.344%   $119.6602   $119.66   $119.65   $119.70  
  Purchase #7 $42.98   8.221%   $46.5134   $46.51   $46.50   $46.50  
  7 purchase totals = $926.35       $994.7227   $994.71   $994.65   $994.80