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 $73.95   3.491%   $76.5316   $76.53   $76.55   $76.50  
  Purchase #2 $228.48   9.258%   $249.6327   $249.63   $249.65   $249.60  
  Purchase #3 $140.66   12.198%   $157.8177   $157.82   $157.80   $157.80  
  Purchase #4 $238.50   10.464%   $263.4566   $263.46   $263.45   $263.50  
  Purchase #5 $204.36   5.150%   $214.8845   $214.88   $214.90   $214.90  
  Purchase #6 $77.58   8.236%   $83.9695   $83.97   $83.95   $84.00  
  Purchase #7 $203.39   9.534%   $222.7812   $222.78   $222.80   $222.80  
  7 purchase totals = $1,166.92       $1,269.0738   $1,269.07   $1,269.10   $1,269.10