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 $117.35   5.781%   $124.134   $124.13   $124.15   $124.10  
  Purchase #2 $9.29   11.814%   $10.3875   $10.39   $10.40   $10.40  
  Purchase #3 $151.53   4.873%   $158.9141   $158.91   $158.90   $158.90  
  Purchase #4 $43.99   6.383%   $46.7979   $46.80   $46.80   $46.80  
  Purchase #5 $82.35   13.316%   $93.3157   $93.32   $93.30   $93.30  
  Purchase #6 $228.28   5.222%   $240.2008   $240.20   $240.20   $240.20  
  Purchase #7 $86.52   10.118%   $95.2741   $95.27   $95.25   $95.30  
  7 purchase totals = $719.31       $769.0241   $769.02   $769.00   $769.00