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 $14.75   8.600%   $16.0185   $16.02   $16.00   $16.00  
  Purchase #2 $139.99   4.829%   $146.7501   $146.75   $146.75   $146.80  
  Purchase #3 $96.36   3.667%   $99.8935   $99.89   $99.90   $99.90  
  Purchase #4 $235.84   5.456%   $248.7074   $248.71   $248.70   $248.70  
  Purchase #5 $57.54   7.295%   $61.7375   $61.74   $61.75   $61.70  
  Purchase #6 $132.92   11.470%   $148.1659   $148.17   $148.15   $148.20  
  Purchase #7 $198.55   7.636%   $213.7113   $213.71   $213.70   $213.70  
  7 purchase totals = $875.95       $934.9842   $934.99   $934.95   $935.00