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 $227.36   5.837%   $240.631   $240.63   $240.65   $240.60  
  Purchase #2 $132.82   4.544%   $138.8553   $138.86   $138.85   $138.90  
  Purchase #3 $50.97   6.134%   $54.0965   $54.10   $54.10   $54.10  
  Purchase #4 $186.68   10.524%   $206.3262   $206.33   $206.35   $206.30  
  Purchase #5 $248.40   10.821%   $275.2794   $275.28   $275.30   $275.30  
  Purchase #6 $228.37   8.373%   $247.4914   $247.49   $247.50   $247.50  
  Purchase #7 $78.62   8.376%   $85.2052   $85.21   $85.20   $85.20  
  7 purchase totals = $1,153.22       $1,247.8850   $1,247.90   $1,247.95   $1,247.90