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 $84.77   13.545%   $96.2521   $96.25   $96.25   $96.30  
  Purchase #2 $250.42   12.289%   $281.1941   $281.19   $281.20   $281.20  
  Purchase #3 $190.34   8.225%   $205.9955   $206.00   $206.00   $206.00  
  Purchase #4 $119.58   3.488%   $123.751   $123.75   $123.75   $123.80  
  Purchase #5 $236.65   8.457%   $256.6635   $256.66   $256.65   $256.70  
  Purchase #6 $111.94   13.173%   $126.6859   $126.69   $126.70   $126.70  
  Purchase #7 $153.42   6.203%   $162.9366   $162.94   $162.95   $162.90  
  7 purchase totals = $1,147.12       $1,253.4787   $1,253.48   $1,253.50   $1,253.60