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 $62.28   13.286%   $70.5545   $70.55   $70.55   $70.60  
  Purchase #2 $156.97   9.278%   $171.5337   $171.53   $171.55   $171.50  
  Purchase #3 $202.82   10.385%   $223.8829   $223.88   $223.90   $223.90  
  Purchase #4 $92.49   3.608%   $95.827   $95.83   $95.85   $95.80  
  Purchase #5 $60.38   5.662%   $63.7987   $63.80   $63.80   $63.80  
  Purchase #6 $60.46   4.537%   $63.2031   $63.20   $63.20   $63.20  
  Purchase #7 $95.63   5.850%   $101.2244   $101.22   $101.20   $101.20  
  7 purchase totals = $731.03       $790.0243   $790.01   $790.05   $790.00