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 $232.47   6.211%   $246.9087   $246.91   $246.90   $246.90  
  Purchase #2 $133.27   9.765%   $146.2838   $146.28   $146.30   $146.30  
  Purchase #3 $127.27   6.113%   $135.05   $135.05   $135.05   $135.10  
  Purchase #4 $100.25   7.584%   $107.853   $107.85   $107.85   $107.90  
  Purchase #5 $62.78   10.454%   $69.343   $69.34   $69.35   $69.30  
  Purchase #6 $206.70   12.722%   $232.9964   $233.00   $233.00   $233.00  
  Purchase #7 $100.73   13.769%   $114.5995   $114.60   $114.60   $114.60  
  7 purchase totals = $963.47       $1,053.0344   $1,053.03   $1,053.05   $1,053.10