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 $59.93   8.800%   $65.2038   $65.20   $65.20   $65.20  
  Purchase #2 $79.77   3.508%   $82.5683   $82.57   $82.55   $82.60  
  Purchase #3 $51.74   11.508%   $57.6942   $57.69   $57.70   $57.70  
  Purchase #4 $161.41   4.793%   $169.1464   $169.15   $169.15   $169.10  
  Purchase #5 $237.35   4.219%   $247.3638   $247.36   $247.35   $247.40  
  Purchase #6 $146.45   10.225%   $161.4245   $161.42   $161.40   $161.40  
  Purchase #7 $95.95   7.317%   $102.9707   $102.97   $102.95   $103.00  
  7 purchase totals = $832.60       $886.3717   $886.36   $886.30   $886.40