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 $34.93   4.808%   $36.6094   $36.61   $36.60   $36.60  
  Purchase #2 $184.40   12.599%   $207.6326   $207.63   $207.65   $207.60  
  Purchase #3 $235.38   5.841%   $249.1285   $249.13   $249.15   $249.10  
  Purchase #4 $185.98   10.486%   $205.4819   $205.48   $205.50   $205.50  
  Purchase #5 $70.83   4.538%   $74.0443   $74.04   $74.05   $74.00  
  Purchase #6 $100.36   4.510%   $104.8862   $104.89   $104.90   $104.90  
  Purchase #7 $13.38   8.163%   $14.4722   $14.47   $14.45   $14.50  
  7 purchase totals = $825.26       $892.2551   $892.25   $892.30   $892.20