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 $66.76   5.350%   $70.3317   $70.33   $70.35   $70.30  
  Purchase #2 $177.28   4.748%   $185.6973   $185.70   $185.70   $185.70  
  Purchase #3 $73.35   3.784%   $76.1256   $76.13   $76.15   $76.10  
  Purchase #4 $92.92   11.776%   $103.8623   $103.86   $103.85   $103.90  
  Purchase #5 $248.96   11.198%   $276.8385   $276.84   $276.85   $276.80  
  Purchase #6 $76.37   10.327%   $84.2567   $84.26   $84.25   $84.30  
  Purchase #7 $165.59   3.417%   $171.2482   $171.25   $171.25   $171.20  
  7 purchase totals = $901.23       $968.3603   $968.37   $968.40   $968.30