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 $211.52   12.143%   $237.2049   $237.20   $237.20   $237.20  
  Purchase #2 $89.63   8.218%   $96.9958   $97.00   $97.00   $97.00  
  Purchase #3 $96.95   4.466%   $101.2798   $101.28   $101.30   $101.30  
  Purchase #4 $108.97   3.703%   $113.0052   $113.01   $113.00   $113.00  
  Purchase #5 $233.98   9.398%   $255.9694   $255.97   $255.95   $256.00  
  Purchase #6 $135.67   7.674%   $146.0813   $146.08   $146.10   $146.10  
  Purchase #7 $8.88   11.767%   $9.9249   $9.92   $9.90   $9.90  
  7 purchase totals = $885.60       $960.4613   $960.46   $960.45   $960.50