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 $188.80   8.752%   $205.3238   $205.32   $205.30   $205.30  
  Purchase #2 $138.99   7.519%   $149.4407   $149.44   $149.45   $149.40  
  Purchase #3 $67.46   11.176%   $74.9993   $75.00   $75.00   $75.00  
  Purchase #4 $58.33   11.763%   $65.1914   $65.19   $65.20   $65.20  
  Purchase #5 $230.41   5.562%   $243.2254   $243.23   $243.25   $243.20  
  Purchase #6 $125.84   4.299%   $131.2499   $131.25   $131.25   $131.20  
  Purchase #7 $119.42   9.289%   $130.5129   $130.51   $130.50   $130.50  
  7 purchase totals = $929.25       $999.9434   $999.94   $999.95   $999.80