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 $203.82   13.298%   $230.924   $230.92   $230.90   $230.90  
  Purchase #2 $119.62   11.161%   $132.9708   $132.97   $132.95   $133.00  
  Purchase #3 $190.62   10.701%   $211.0182   $211.02   $211.00   $211.00  
  Purchase #4 $235.92   5.464%   $248.8107   $248.81   $248.80   $248.80  
  Purchase #5 $163.37   13.313%   $185.1194   $185.12   $185.10   $185.10  
  Purchase #6 $67.43   7.201%   $72.2856   $72.29   $72.30   $72.30  
  Purchase #7 $139.42   10.792%   $154.4662   $154.47   $154.45   $154.50  
  7 purchase totals = $1,120.20       $1,235.5949   $1,235.60   $1,235.50   $1,235.60