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 $243.36   7.823%   $262.3981   $262.40   $262.40   $262.40  
  Purchase #2 $154.88   6.769%   $165.3638   $165.36   $165.35   $165.40  
  Purchase #3 $187.63   12.291%   $210.6916   $210.69   $210.70   $210.70  
  Purchase #4 $130.35   3.283%   $134.6294   $134.63   $134.65   $134.60  
  Purchase #5 $249.98   8.497%   $271.2208   $271.22   $271.20   $271.20  
  Purchase #6 $108.97   5.227%   $114.6659   $114.67   $114.65   $114.70  
  Purchase #7 $117.92   5.799%   $124.7582   $124.76   $124.75   $124.80  
  7 purchase totals = $1,193.09       $1,283.7278   $1,283.73   $1,283.70   $1,283.80