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 $60.41   9.729%   $66.2873   $66.29   $66.30   $66.30  
  Purchase #2 $160.65   6.429%   $170.9782   $170.98   $171.00   $171.00  
  Purchase #3 $114.95   13.431%   $130.3889   $130.39   $130.40   $130.40  
  Purchase #4 $237.98   12.364%   $267.4038   $267.40   $267.40   $267.40  
  Purchase #5 $107.58   8.785%   $117.0309   $117.03   $117.05   $117.00  
  Purchase #6 $36.54   13.516%   $41.4787   $41.48   $41.50   $41.50  
  Purchase #7 $163.90   3.824%   $170.1675   $170.17   $170.15   $170.20  
  7 purchase totals = $882.01       $963.7353   $963.74   $963.80   $963.80