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 $237.92   6.748%   $253.9748   $253.97   $253.95   $254.00  
  Purchase #2 $62.63   4.201%   $65.2611   $65.26   $65.25   $65.30  
  Purchase #3 $53.99   11.405%   $60.1476   $60.15   $60.15   $60.10  
  Purchase #4 $179.55   3.127%   $185.1645   $185.16   $185.15   $185.20  
  Purchase #5 $84.33   9.469%   $92.3152   $92.32   $92.30   $92.30  
  Purchase #6 $141.36   9.442%   $154.7072   $154.71   $154.70   $154.70  
  Purchase #7 $109.93   6.482%   $117.0557   $117.06   $117.05   $117.10  
  7 purchase totals = $869.71       $928.6261   $928.63   $928.55   $928.70