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 $68.38   6.694%   $72.9574   $72.96   $72.95   $73.00  
  Purchase #2 $64.35   6.652%   $68.6306   $68.63   $68.65   $68.60  
  Purchase #3 $125.31   9.627%   $137.3736   $137.37   $137.35   $137.40  
  Purchase #4 $93.65   4.164%   $97.5496   $97.55   $97.55   $97.50  
  Purchase #5 $63.97   3.366%   $66.1232   $66.12   $66.10   $66.10  
  Purchase #6 $83.47   13.732%   $94.9321   $94.93   $94.95   $94.90  
  Purchase #7 $197.31   12.446%   $221.8672   $221.87   $221.85   $221.90  
  7 purchase totals = $696.44       $759.4337   $759.43   $759.40   $759.40