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 $34.60   4.610%   $36.1951   $36.20   $36.20   $36.20  
  Purchase #2 $147.99   12.796%   $166.9268   $166.93   $166.95   $166.90  
  Purchase #3 $87.35   11.472%   $97.3708   $97.37   $97.35   $97.40  
  Purchase #4 $113.65   3.198%   $117.2845   $117.28   $117.30   $117.30  
  Purchase #5 $248.41   7.612%   $267.319   $267.32   $267.30   $267.30  
  Purchase #6 $173.43   11.565%   $193.4872   $193.49   $193.50   $193.50  
  Purchase #7 $76.52   11.844%   $85.583   $85.58   $85.60   $85.60  
  7 purchase totals = $881.95       $964.1664   $964.17   $964.20   $964.20