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 $150.98   12.353%   $169.6306   $169.63   $169.65   $169.60  
  Purchase #2 $122.95   10.430%   $135.7737   $135.77   $135.75   $135.80  
  Purchase #3 $33.56   9.136%   $36.626   $36.63   $36.65   $36.60  
  Purchase #4 $92.86   4.768%   $97.2876   $97.29   $97.30   $97.30  
  Purchase #5 $205.93   6.159%   $218.6132   $218.61   $218.60   $218.60  
  Purchase #6 $190.36   7.208%   $204.0811   $204.08   $204.10   $204.10  
  Purchase #7 $63.41   11.596%   $70.763   $70.76   $70.75   $70.80  
  7 purchase totals = $860.05       $932.7752   $932.77   $932.80   $932.80