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 $67.75   12.591%   $76.2804   $76.28   $76.30   $76.30  
  Purchase #2 $158.68   7.715%   $170.9222   $170.92   $170.90   $170.90  
  Purchase #3 $25.70   4.721%   $26.9133   $26.91   $26.90   $26.90  
  Purchase #4 $92.70   7.607%   $99.7517   $99.75   $99.75   $99.80  
  Purchase #5 $145.74   12.212%   $163.5378   $163.54   $163.55   $163.50  
  Purchase #6 $96.88   7.777%   $104.4144   $104.41   $104.40   $104.40  
  Purchase #7 $116.68   7.308%   $125.207   $125.21   $125.20   $125.20  
  7 purchase totals = $704.13       $767.0268   $767.02   $767.00   $767.00