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 $24.65   3.872%   $25.6044   $25.60   $25.60   $25.60  
  Purchase #2 $74.96   13.686%   $85.219   $85.22   $85.20   $85.20  
  Purchase #3 $245.79   4.470%   $256.7768   $256.78   $256.80   $256.80  
  Purchase #4 $206.69   9.782%   $226.9084   $226.91   $226.90   $226.90  
  Purchase #5 $114.73   9.843%   $126.0229   $126.02   $126.00   $126.00  
  Purchase #6 $115.76   6.859%   $123.7   $123.70   $123.70   $123.70  
  Purchase #7 $5.44   12.256%   $6.1067   $6.11   $6.10   $6.10  
  7 purchase totals = $788.02       $850.3382   $850.34   $850.30   $850.30