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 $48.93   4.244%   $51.0066   $51.01   $51.00   $51.00  
  Purchase #2 $195.31   9.265%   $213.4055   $213.41   $213.40   $213.40  
  Purchase #3 $19.65   10.363%   $21.6863   $21.69   $21.70   $21.70  
  Purchase #4 $18.43   4.577%   $19.2735   $19.27   $19.25   $19.30  
  Purchase #5 $67.53   11.573%   $75.3452   $75.35   $75.35   $75.30  
  Purchase #6 $151.62   5.271%   $159.6119   $159.61   $159.60   $159.60  
  Purchase #7 $203.84   11.202%   $226.6742   $226.67   $226.65   $226.70  
  7 purchase totals = $705.31       $767.0032   $767.01   $766.95   $767.00