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 $48.81   8.318%   $52.87   $52.87   $52.85   $52.90  
  Purchase #2 $93.35   10.185%   $102.8577   $102.86   $102.85   $102.90  
  Purchase #3 $76.76   4.134%   $79.9333   $79.93   $79.95   $79.90  
  Purchase #4 $139.85   4.558%   $146.2244   $146.22   $146.20   $146.20  
  Purchase #5 $179.61   11.514%   $200.2903   $200.29   $200.30   $200.30  
  Purchase #6 $43.54   12.443%   $48.9577   $48.96   $48.95   $49.00  
  Purchase #7 $115.32   4.787%   $120.8404   $120.84   $120.85   $120.80  
  7 purchase totals = $697.24       $751.9738   $751.97   $751.95   $752.00