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 $219.55   10.247%   $242.0473   $242.05   $242.05   $242.00  
  Purchase #2 $210.42   3.737%   $218.2834   $218.28   $218.30   $218.30  
  Purchase #3 $148.92   3.400%   $153.9833   $153.98   $154.00   $154.00  
  Purchase #4 $24.90   6.277%   $26.463   $26.46   $26.45   $26.50  
  Purchase #5 $141.30   9.283%   $154.4169   $154.42   $154.40   $154.40  
  Purchase #6 $192.25   3.767%   $199.4921   $199.49   $199.50   $199.50  
  Purchase #7 $136.82   12.548%   $153.9882   $153.99   $154.00   $154.00  
  7 purchase totals = $1,074.16       $1,148.6742   $1,148.67   $1,148.70   $1,148.70