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 $116.56   9.636%   $127.7917   $127.79   $127.80   $127.80  
  Purchase #2 $159.25   4.652%   $166.6583   $166.66   $166.65   $166.70  
  Purchase #3 $167.83   5.164%   $176.4967   $176.50   $176.50   $176.50  
  Purchase #4 $242.46   6.687%   $258.6733   $258.67   $258.65   $258.70  
  Purchase #5 $170.67   8.441%   $185.0763   $185.08   $185.10   $185.10  
  Purchase #6 $26.60   6.201%   $28.2495   $28.25   $28.25   $28.20  
  Purchase #7 $18.99   5.198%   $19.9771   $19.98   $20.00   $20.00  
  7 purchase totals = $902.36       $962.9229   $962.93   $962.95   $963.00