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 $53.29   7.437%   $57.2532   $57.25   $57.25   $57.30  
  Purchase #2 $126.75   8.567%   $137.6087   $137.61   $137.60   $137.60  
  Purchase #3 $196.52   4.293%   $204.9566   $204.96   $204.95   $205.00  
  Purchase #4 $32.76   12.569%   $36.8776   $36.88   $36.90   $36.90  
  Purchase #5 $112.77   3.166%   $116.3403   $116.34   $116.35   $116.30  
  Purchase #6 $239.86   9.348%   $262.2821   $262.28   $262.30   $262.30  
  Purchase #7 $66.44   7.278%   $71.2755   $71.28   $71.30   $71.30  
  7 purchase totals = $828.39       $886.5940   $886.60   $886.65   $886.70