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 $12.95   7.738%   $13.9521   $13.95   $13.95   $14.00  
  Purchase #2 $84.39   12.849%   $95.2333   $95.23   $95.25   $95.20  
  Purchase #3 $59.96   13.867%   $68.2747   $68.27   $68.25   $68.30  
  Purchase #4 $161.51   6.143%   $171.4316   $171.43   $171.45   $171.40  
  Purchase #5 $26.42   13.562%   $30.0031   $30.00   $30.00   $30.00  
  Purchase #6 $123.42   5.560%   $130.2822   $130.28   $130.30   $130.30  
  Purchase #7 $33.48   8.463%   $36.3134   $36.31   $36.30   $36.30  
  7 purchase totals = $502.13       $545.4904   $545.47   $545.50   $545.50