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 $223.99   10.424%   $247.3387   $247.34   $247.35   $247.30  
  Purchase #2 $117.41   5.268%   $123.5952   $123.60   $123.60   $123.60  
  Purchase #3 $230.87   10.231%   $254.4903   $254.49   $254.50   $254.50  
  Purchase #4 $58.48   6.832%   $62.4754   $62.48   $62.50   $62.50  
  Purchase #5 $176.91   12.622%   $199.2396   $199.24   $199.25   $199.20  
  Purchase #6 $169.97   7.707%   $183.0696   $183.07   $183.05   $183.10  
  Purchase #7 $198.85   13.478%   $225.651   $225.65   $225.65   $225.70  
  7 purchase totals = $1,176.48       $1,295.8598   $1,295.87   $1,295.90   $1,295.90