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 $94.35   4.457%   $98.5552   $98.56   $98.55   $98.60  
  Purchase #2 $125.62   6.801%   $134.1634   $134.16   $134.15   $134.20  
  Purchase #3 $160.84   5.424%   $169.564   $169.56   $169.55   $169.60  
  Purchase #4 $13.47   6.767%   $14.3815   $14.38   $14.40   $14.40  
  Purchase #5 $27.75   12.625%   $31.2534   $31.25   $31.25   $31.30  
  Purchase #6 $188.30   11.316%   $209.608   $209.61   $209.60   $209.60  
  Purchase #7 $124.86   11.136%   $138.7644   $138.76   $138.75   $138.80  
  7 purchase totals = $735.19       $796.2899   $796.28   $796.25   $796.50