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 $59.31   8.353%   $64.2642   $64.26   $64.25   $64.30  
  Purchase #2 $117.36   5.338%   $123.6247   $123.62   $123.60   $123.60  
  Purchase #3 $64.40   13.283%   $72.9543   $72.95   $72.95   $73.00  
  Purchase #4 $152.44   11.425%   $169.8563   $169.86   $169.85   $169.90  
  Purchase #5 $68.96   6.270%   $73.2838   $73.28   $73.30   $73.30  
  Purchase #6 $55.77   9.243%   $60.9248   $60.92   $60.90   $60.90  
  Purchase #7 $240.74   10.818%   $266.7833   $266.78   $266.80   $266.80  
  7 purchase totals = $758.98       $831.6914   $831.67   $831.65   $831.80