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 $40.25   7.507%   $43.2716   $43.27   $43.25   $43.30  
  Purchase #2 $177.92   6.282%   $189.0969   $189.10   $189.10   $189.10  
  Purchase #3 $143.84   8.550%   $156.1383   $156.14   $156.15   $156.10  
  Purchase #4 $140.96   12.588%   $158.704   $158.70   $158.70   $158.70  
  Purchase #5 $154.38   3.434%   $159.6814   $159.68   $159.70   $159.70  
  Purchase #6 $45.66   11.769%   $51.0337   $51.03   $51.05   $51.00  
  Purchase #7 $171.42   4.158%   $178.5476   $178.55   $178.55   $178.50  
  7 purchase totals = $874.43       $936.4735   $936.47   $936.50   $936.40