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 $226.92   9.498%   $248.4729   $248.47   $248.45   $248.50  
  Purchase #2 $147.39   7.161%   $157.9446   $157.94   $157.95   $157.90  
  Purchase #3 $186.87   5.616%   $197.3646   $197.36   $197.35   $197.40  
  Purchase #4 $148.55   12.327%   $166.8618   $166.86   $166.85   $166.90  
  Purchase #5 $83.86   10.609%   $92.7567   $92.76   $92.75   $92.80  
  Purchase #6 $241.51   5.311%   $254.3366   $254.34   $254.35   $254.30  
  Purchase #7 $172.54   7.560%   $185.584   $185.58   $185.60   $185.60  
  7 purchase totals = $1,207.64       $1,303.3212   $1,303.31   $1,303.30   $1,303.40