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 $227.76   7.347%   $244.4935   $244.49   $244.50   $244.50  
  Purchase #2 $134.67   4.760%   $141.0803   $141.08   $141.10   $141.10  
  Purchase #3 $214.57   9.396%   $234.731   $234.73   $234.75   $234.70  
  Purchase #4 $30.86   6.177%   $32.7662   $32.77   $32.75   $32.80  
  Purchase #5 $165.75   8.821%   $180.3708   $180.37   $180.35   $180.40  
  Purchase #6 $177.44   10.551%   $196.1617   $196.16   $196.15   $196.20  
  Purchase #7 $215.66   3.782%   $223.8163   $223.82   $223.80   $223.80  
  7 purchase totals = $1,166.71       $1,253.4198   $1,253.42   $1,253.40   $1,253.50