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 $111.95   12.326%   $125.749   $125.75   $125.75   $125.70  
  Purchase #2 $59.65   12.663%   $67.2035   $67.20   $67.20   $67.20  
  Purchase #3 $195.62   12.283%   $219.648   $219.65   $219.65   $219.60  
  Purchase #4 $84.37   8.768%   $91.7676   $91.77   $91.75   $91.80  
  Purchase #5 $226.74   12.179%   $254.3547   $254.35   $254.35   $254.40  
  Purchase #6 $144.85   9.673%   $158.8613   $158.86   $158.85   $158.90  
  Purchase #7 $9.46   7.698%   $10.1882   $10.19   $10.20   $10.20  
  7 purchase totals = $832.64       $927.7723   $927.77   $927.75   $927.80