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 $40.62   8.687%   $44.1487   $44.15   $44.15   $44.10  
  Purchase #2 $214.34   10.305%   $236.4277   $236.43   $236.45   $236.40  
  Purchase #3 $197.26   3.379%   $203.9254   $203.93   $203.95   $203.90  
  Purchase #4 $126.60   4.173%   $131.883   $131.88   $131.90   $131.90  
  Purchase #5 $183.27   12.749%   $206.6351   $206.64   $206.65   $206.60  
  Purchase #6 $163.31   8.744%   $177.5898   $177.59   $177.60   $177.60  
  Purchase #7 $232.77   8.708%   $253.0396   $253.04   $253.05   $253.00  
  7 purchase totals = $1,158.17       $1,253.6493   $1,253.66   $1,253.75   $1,253.50