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 $235.80   13.387%   $267.3665   $267.37   $267.35   $267.40  
  Purchase #2 $93.99   10.760%   $104.1033   $104.10   $104.10   $104.10  
  Purchase #3 $195.66   6.170%   $207.7322   $207.73   $207.75   $207.70  
  Purchase #4 $14.25   11.302%   $15.8605   $15.86   $15.85   $15.90  
  Purchase #5 $7.63   12.111%   $8.5541   $8.55   $8.55   $8.60  
  Purchase #6 $205.27   8.731%   $223.1921   $223.19   $223.20   $223.20  
  Purchase #7 $126.65   8.313%   $137.1784   $137.18   $137.20   $137.20  
  7 purchase totals = $879.25       $963.9871   $963.98   $964.00   $964.10