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 $84.50   12.227%   $94.8318   $94.83   $94.85   $94.80  
  Purchase #2 $136.71   10.157%   $150.5956   $150.60   $150.60   $150.60  
  Purchase #3 $235.55   12.291%   $264.5015   $264.50   $264.50   $264.50  
  Purchase #4 $68.94   9.263%   $75.3259   $75.33   $75.35   $75.30  
  Purchase #5 $18.92   8.196%   $20.4707   $20.47   $20.45   $20.50  
  Purchase #6 $202.82   10.808%   $224.7408   $224.74   $224.75   $224.70  
  Purchase #7 $90.50   7.563%   $97.3445   $97.34   $97.35   $97.30  
  7 purchase totals = $837.94       $927.8108   $927.81   $927.85   $927.70