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 $82.95   12.559%   $93.3677   $93.37   $93.35   $93.40  
  Purchase #2 $13.69   6.811%   $14.6224   $14.62   $14.60   $14.60  
  Purchase #3 $224.28   4.206%   $233.7132   $233.71   $233.70   $233.70  
  Purchase #4 $47.60   13.559%   $54.0541   $54.05   $54.05   $54.10  
  Purchase #5 $156.48   6.204%   $166.188   $166.19   $166.20   $166.20  
  Purchase #6 $159.28   7.192%   $170.7354   $170.74   $170.75   $170.70  
  Purchase #7 $18.74   7.536%   $20.1522   $20.15   $20.15   $20.20  
  7 purchase totals = $703.02       $752.8330   $752.83   $752.80   $752.90