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 $245.64   6.391%   $261.3389   $261.34   $261.35   $261.30  
  Purchase #2 $212.94   13.341%   $241.3483   $241.35   $241.35   $241.30  
  Purchase #3 $148.32   12.149%   $166.3394   $166.34   $166.35   $166.30  
  Purchase #4 $34.44   4.348%   $35.9375   $35.94   $35.95   $35.90  
  Purchase #5 $168.31   7.832%   $181.492   $181.49   $181.50   $181.50  
  Purchase #6 $183.73   7.643%   $197.7725   $197.77   $197.75   $197.80  
  Purchase #7 $234.46   3.276%   $242.1409   $242.14   $242.15   $242.10  
  7 purchase totals = $1,227.84       $1,326.3695   $1,326.37   $1,326.40   $1,326.20