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 $59.54   7.332%   $63.9055   $63.91   $63.90   $63.90  
  Purchase #2 $30.90   10.347%   $34.0972   $34.10   $34.10   $34.10  
  Purchase #3 $188.79   12.557%   $212.4964   $212.50   $212.50   $212.50  
  Purchase #4 $11.61   5.315%   $12.2271   $12.23   $12.25   $12.20  
  Purchase #5 $100.27   13.103%   $113.4084   $113.41   $113.40   $113.40  
  Purchase #6 $74.88   6.802%   $79.9733   $79.97   $79.95   $80.00  
  Purchase #7 $216.40   11.134%   $240.494   $240.49   $240.50   $240.50  
  7 purchase totals = $682.39       $756.6019   $756.61   $756.60   $756.60