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 $41.79   11.343%   $46.5302   $46.53   $46.55   $46.50  
  Purchase #2 $149.93   10.527%   $165.7131   $165.71   $165.70   $165.70  
  Purchase #3 $83.45   6.495%   $88.8701   $88.87   $88.85   $88.90  
  Purchase #4 $201.94   13.334%   $228.8667   $228.87   $228.85   $228.90  
  Purchase #5 $172.88   13.102%   $195.5307   $195.53   $195.55   $195.50  
  Purchase #6 $44.46   5.526%   $46.9169   $46.92   $46.90   $46.90  
  Purchase #7 $99.85   12.456%   $112.2873   $112.29   $112.30   $112.30  
  7 purchase totals = $794.30       $884.7150   $884.72   $884.70   $884.70