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 $242.60   8.836%   $264.0361   $264.04   $264.05   $264.00  
  Purchase #2 $49.63   6.417%   $52.8148   $52.81   $52.80   $52.80  
  Purchase #3 $105.75   4.234%   $110.2275   $110.23   $110.25   $110.20  
  Purchase #4 $48.61   3.811%   $50.4625   $50.46   $50.45   $50.50  
  Purchase #5 $147.43   4.389%   $153.9007   $153.90   $153.90   $153.90  
  Purchase #6 $94.95   4.750%   $99.4601   $99.46   $99.45   $99.50  
  Purchase #7 $5.38   9.650%   $5.8992   $5.90   $5.90   $5.90  
  7 purchase totals = $694.35       $736.8009   $736.80   $736.80   $736.80