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 $205.55   13.313%   $232.9149   $232.91   $232.90   $232.90  
  Purchase #2 $168.72   11.629%   $188.3404   $188.34   $188.35   $188.30  
  Purchase #3 $239.64   13.602%   $272.2358   $272.24   $272.25   $272.20  
  Purchase #4 $177.40   12.205%   $199.0517   $199.05   $199.05   $199.10  
  Purchase #5 $77.91   6.667%   $83.1043   $83.10   $83.10   $83.10  
  Purchase #6 $243.42   7.585%   $261.8834   $261.88   $261.90   $261.90  
  Purchase #7 $9.61   12.865%   $10.8463   $10.85   $10.85   $10.80  
  7 purchase totals = $1,122.25       $1,248.3768   $1,248.37   $1,248.40   $1,248.30