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 $218.91   12.622%   $246.5408   $246.54   $246.55   $246.50  
  Purchase #2 $194.89   10.577%   $215.5035   $215.50   $215.50   $215.50  
  Purchase #3 $136.87   9.465%   $149.8247   $149.82   $149.80   $149.80  
  Purchase #4 $154.53   8.850%   $168.2059   $168.21   $168.20   $168.20  
  Purchase #5 $242.77   8.376%   $263.1044   $263.10   $263.10   $263.10  
  Purchase #6 $10.31   5.867%   $10.9149   $10.91   $10.90   $10.90  
  Purchase #7 $57.67   7.519%   $62.0062   $62.01   $62.00   $62.00  
  7 purchase totals = $1,015.95       $1,116.1004   $1,116.09   $1,116.05   $1,116.00