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 $43.56   13.777%   $49.5613   $49.56   $49.55   $49.60  
  Purchase #2 $66.52   4.237%   $69.3385   $69.34   $69.35   $69.30  
  Purchase #3 $244.36   9.479%   $267.5229   $267.52   $267.50   $267.50  
  Purchase #4 $168.27   8.762%   $183.0138   $183.01   $183.00   $183.00  
  Purchase #5 $147.95   7.712%   $159.3599   $159.36   $159.35   $159.40  
  Purchase #6 $133.29   13.408%   $151.1615   $151.16   $151.15   $151.20  
  Purchase #7 $104.51   12.223%   $117.2843   $117.28   $117.30   $117.30  
  7 purchase totals = $908.46       $997.2422   $997.23   $997.20   $997.30