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 $53.82   9.486%   $58.9254   $58.93   $58.95   $58.90  
  Purchase #2 $232.51   5.214%   $244.6331   $244.63   $244.65   $244.60  
  Purchase #3 $59.72   5.121%   $62.7783   $62.78   $62.80   $62.80  
  Purchase #4 $94.68   5.339%   $99.735   $99.74   $99.75   $99.70  
  Purchase #5 $205.44   7.606%   $221.0658   $221.07   $221.05   $221.10  
  Purchase #6 $110.86   13.586%   $125.9214   $125.92   $125.90   $125.90  
  Purchase #7 $164.91   9.709%   $180.9211   $180.92   $180.90   $180.90  
  7 purchase totals = $921.94       $993.9801   $993.99   $994.00   $993.90