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 $65.56   12.562%   $73.7956   $73.80   $73.80   $73.80  
  Purchase #2 $212.46   9.677%   $233.0198   $233.02   $233.00   $233.00  
  Purchase #3 $93.35   12.171%   $104.7116   $104.71   $104.70   $104.70  
  Purchase #4 $204.25   9.779%   $224.2236   $224.22   $224.20   $224.20  
  Purchase #5 $142.37   5.318%   $149.9412   $149.94   $149.95   $149.90  
  Purchase #6 $16.91   5.456%   $17.8326   $17.83   $17.85   $17.80  
  Purchase #7 $29.38   10.491%   $32.4623   $32.46   $32.45   $32.50  
  7 purchase totals = $764.28       $835.9867   $835.98   $835.95   $835.90