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 $47.94   11.516%   $53.4608   $53.46   $53.45   $53.50  
  Purchase #2 $217.83   7.699%   $234.6007   $234.60   $234.60   $234.60  
  Purchase #3 $71.97   5.420%   $75.8708   $75.87   $75.85   $75.90  
  Purchase #4 $188.66   12.824%   $212.8538   $212.85   $212.85   $212.90  
  Purchase #5 $186.27   12.271%   $209.1272   $209.13   $209.15   $209.10  
  Purchase #6 $76.26   13.454%   $86.52   $86.52   $86.50   $86.50  
  Purchase #7 $110.33   9.243%   $120.5278   $120.53   $120.55   $120.50  
  7 purchase totals = $899.26       $992.9611   $992.96   $992.95   $993.00