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 $57.28   8.166%   $61.9575   $61.96   $61.95   $62.00  
  Purchase #2 $55.72   11.699%   $62.2387   $62.24   $62.25   $62.20  
  Purchase #3 $133.40   11.453%   $148.6783   $148.68   $148.70   $148.70  
  Purchase #4 $12.38   6.446%   $13.178   $13.18   $13.20   $13.20  
  Purchase #5 $183.97   7.783%   $198.2884   $198.29   $198.30   $198.30  
  Purchase #6 $73.46   3.130%   $75.7593   $75.76   $75.75   $75.80  
  Purchase #7 $139.88   8.500%   $151.7698   $151.77   $151.75   $151.80  
  7 purchase totals = $656.09       $711.8700   $711.88   $711.90   $712.00