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 $67.37   13.242%   $76.2911   $76.29   $76.30   $76.30  
  Purchase #2 $155.89   9.173%   $170.1898   $170.19   $170.20   $170.20  
  Purchase #3 $115.33   8.784%   $125.4606   $125.46   $125.45   $125.50  
  Purchase #4 $96.64   7.536%   $103.9228   $103.92   $103.90   $103.90  
  Purchase #5 $175.42   4.423%   $183.1788   $183.18   $183.20   $183.20  
  Purchase #6 $86.80   4.328%   $90.5567   $90.56   $90.55   $90.60  
  Purchase #7 $108.44   9.489%   $118.7299   $118.73   $118.75   $118.70  
  7 purchase totals = $805.89       $868.3297   $868.33   $868.35   $868.40