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 $195.39   5.381%   $205.9039   $205.90   $205.90   $205.90  
  Purchase #2 $91.26   11.275%   $101.5496   $101.55   $101.55   $101.50  
  Purchase #3 $166.25   6.327%   $176.7686   $176.77   $176.75   $176.80  
  Purchase #4 $67.96   5.868%   $71.9479   $71.95   $71.95   $71.90  
  Purchase #5 $94.58   10.204%   $104.2309   $104.23   $104.25   $104.20  
  Purchase #6 $149.51   13.635%   $169.8957   $169.90   $169.90   $169.90  
  Purchase #7 $6.35   10.457%   $7.014   $7.01   $7.00   $7.00  
  7 purchase totals = $771.30       $837.3106   $837.31   $837.30   $837.20