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 $81.26   12.729%   $91.6036   $91.60   $91.60   $91.60  
  Purchase #2 $124.43   13.826%   $141.6337   $141.63   $141.65   $141.60  
  Purchase #3 $165.62   6.674%   $176.6735   $176.67   $176.65   $176.70  
  Purchase #4 $48.38   12.475%   $54.4154   $54.42   $54.40   $54.40  
  Purchase #5 $95.65   8.847%   $104.1122   $104.11   $104.10   $104.10  
  Purchase #6 $126.32   13.595%   $143.4932   $143.49   $143.50   $143.50  
  Purchase #7 $227.48   5.852%   $240.7921   $240.79   $240.80   $240.80  
  7 purchase totals = $869.14       $952.7237   $952.71   $952.70   $952.70