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 $56.25   11.234%   $62.5691   $62.57   $62.55   $62.60  
  Purchase #2 $63.95   8.274%   $69.2412   $69.24   $69.25   $69.20  
  Purchase #3 $56.52   3.761%   $58.6457   $58.65   $58.65   $58.60  
  Purchase #4 $76.89   13.145%   $86.9972   $87.00   $87.00   $87.00  
  Purchase #5 $121.95   8.498%   $132.3133   $132.31   $132.30   $132.30  
  Purchase #6 $244.93   6.223%   $260.172   $260.17   $260.15   $260.20  
  Purchase #7 $145.65   3.164%   $150.2584   $150.26   $150.25   $150.30  
  7 purchase totals = $766.14       $820.1969   $820.20   $820.15   $820.20