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 $186.47   4.663%   $195.1651   $195.17   $195.15   $195.20  
  Purchase #2 $203.96   12.538%   $229.5325   $229.53   $229.55   $229.50  
  Purchase #3 $194.64   12.314%   $218.608   $218.61   $218.60   $218.60  
  Purchase #4 $71.83   10.291%   $79.222   $79.22   $79.20   $79.20  
  Purchase #5 $17.55   9.578%   $19.2309   $19.23   $19.25   $19.20  
  Purchase #6 $129.69   13.192%   $146.7987   $146.80   $146.80   $146.80  
  Purchase #7 $239.90   10.406%   $264.864   $264.86   $264.85   $264.90  
  7 purchase totals = $1,044.04       $1,153.4212   $1,153.42   $1,153.40   $1,153.40