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 $68.99   10.681%   $76.3588   $76.36   $76.35   $76.40  
  Purchase #2 $112.76   5.201%   $118.6246   $118.62   $118.60   $118.60  
  Purchase #3 $157.75   11.487%   $175.8707   $175.87   $175.85   $175.90  
  Purchase #4 $190.55   3.367%   $196.9658   $196.97   $196.95   $197.00  
  Purchase #5 $34.52   12.611%   $38.8733   $38.87   $38.85   $38.90  
  Purchase #6 $75.56   8.375%   $81.8882   $81.89   $81.90   $81.90  
  Purchase #7 $226.27   7.541%   $243.333   $243.33   $243.35   $243.30  
  7 purchase totals = $866.40       $931.9144   $931.91   $931.85   $932.00