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 $119.84   13.612%   $136.1526   $136.15   $136.15   $136.20  
  Purchase #2 $231.93   12.319%   $260.5015   $260.50   $260.50   $260.50  
  Purchase #3 $141.42   10.580%   $156.3822   $156.38   $156.40   $156.40  
  Purchase #4 $195.66   10.200%   $215.6173   $215.62   $215.60   $215.60  
  Purchase #5 $124.78   6.524%   $132.9206   $132.92   $132.90   $132.90  
  Purchase #6 $140.31   3.112%   $144.6764   $144.68   $144.70   $144.70  
  Purchase #7 $52.99   5.461%   $55.8838   $55.88   $55.90   $55.90  
  7 purchase totals = $1,006.93       $1,102.1344   $1,102.13   $1,102.15   $1,102.20