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 $69.40   10.207%   $76.4837   $76.48   $76.50   $76.50  
  Purchase #2 $44.60   11.250%   $49.6175   $49.62   $49.60   $49.60  
  Purchase #3 $196.40   11.374%   $218.7385   $218.74   $218.75   $218.70  
  Purchase #4 $125.68   9.699%   $137.8697   $137.87   $137.85   $137.90  
  Purchase #5 $158.86   12.432%   $178.6095   $178.61   $178.60   $178.60  
  Purchase #6 $105.76   6.156%   $112.2706   $112.27   $112.25   $112.30  
  Purchase #7 $54.88   5.559%   $57.9308   $57.93   $57.95   $57.90  
  7 purchase totals = $755.58       $831.5203   $831.52   $831.50   $831.50