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 $184.67   11.343%   $205.6171   $205.62   $205.60   $205.60  
  Purchase #2 $16.65   9.502%   $18.2321   $18.23   $18.25   $18.20  
  Purchase #3 $94.65   8.260%   $102.4681   $102.47   $102.45   $102.50  
  Purchase #4 $178.34   9.318%   $194.9577   $194.96   $194.95   $195.00  
  Purchase #5 $69.30   5.665%   $73.2258   $73.23   $73.25   $73.20  
  Purchase #6 $87.94   12.574%   $98.9976   $99.00   $99.00   $99.00  
  Purchase #7 $75.73   9.518%   $82.938   $82.94   $82.95   $82.90  
  7 purchase totals = $707.28       $776.4364   $776.45   $776.45   $776.40