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 $58.59   4.135%   $61.0127   $61.01   $61.00   $61.00  
  Purchase #2 $209.70   5.747%   $221.7515   $221.75   $221.75   $221.80  
  Purchase #3 $140.93   7.804%   $151.9282   $151.93   $151.95   $151.90  
  Purchase #4 $194.96   10.380%   $215.1968   $215.20   $215.20   $215.20  
  Purchase #5 $185.48   11.745%   $207.2646   $207.26   $207.25   $207.30  
  Purchase #6 $32.75   3.760%   $33.9814   $33.98   $34.00   $34.00  
  Purchase #7 $97.90   7.237%   $104.985   $104.99   $105.00   $105.00  
  7 purchase totals = $920.31       $996.1202   $996.12   $996.15   $996.20