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 $47.97   8.786%   $52.1846   $52.18   $52.20   $52.20  
  Purchase #2 $211.87   9.647%   $232.3091   $232.31   $232.30   $232.30  
  Purchase #3 $6.49   4.536%   $6.7844   $6.78   $6.80   $6.80  
  Purchase #4 $54.50   13.459%   $61.8352   $61.84   $61.85   $61.80  
  Purchase #5 $31.38   13.560%   $35.6351   $35.64   $35.65   $35.60  
  Purchase #6 $51.94   12.482%   $58.4232   $58.42   $58.40   $58.40  
  Purchase #7 $205.57   4.770%   $215.3757   $215.38   $215.40   $215.40  
  7 purchase totals = $609.72       $662.5473   $662.55   $662.60   $662.50