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 $250.63   7.259%   $268.8232   $268.82   $268.80   $268.80  
  Purchase #2 $124.65   13.644%   $141.6572   $141.66   $141.65   $141.70  
  Purchase #3 $156.35   10.656%   $173.0107   $173.01   $173.00   $173.00  
  Purchase #4 $97.81   3.562%   $101.294   $101.29   $101.30   $101.30  
  Purchase #5 $186.45   13.266%   $211.1845   $211.18   $211.20   $211.20  
  Purchase #6 $171.50   13.701%   $194.9972   $195.00   $195.00   $195.00  
  Purchase #7 $50.25   10.402%   $55.477   $55.48   $55.50   $55.50  
  7 purchase totals = $1,037.64       $1,146.4438   $1,146.44   $1,146.45   $1,146.50