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 $14.94   5.277%   $15.7284   $15.73   $15.75   $15.70  
  Purchase #2 $188.95   6.726%   $201.6588   $201.66   $201.65   $201.70  
  Purchase #3 $31.78   9.152%   $34.6885   $34.69   $34.70   $34.70  
  Purchase #4 $84.61   7.804%   $91.213   $91.21   $91.20   $91.20  
  Purchase #5 $118.73   4.600%   $124.1916   $124.19   $124.20   $124.20  
  Purchase #6 $228.36   10.270%   $251.8126   $251.81   $251.80   $251.80  
  Purchase #7 $8.63   12.872%   $9.7409   $9.74   $9.75   $9.70  
  7 purchase totals = $676.00       $729.0338   $729.03   $729.05   $729.00