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 $60.66   8.682%   $65.9265   $65.93   $65.95   $65.90  
  Purchase #2 $232.44   12.450%   $261.3788   $261.38   $261.40   $261.40  
  Purchase #3 $48.72   13.313%   $55.2061   $55.21   $55.20   $55.20  
  Purchase #4 $134.66   13.691%   $153.0963   $153.10   $153.10   $153.10  
  Purchase #5 $199.46   11.510%   $222.4178   $222.42   $222.40   $222.40  
  Purchase #6 $84.74   8.672%   $92.0887   $92.09   $92.10   $92.10  
  Purchase #7 $6.94   3.156%   $7.159   $7.16   $7.15   $7.20  
  7 purchase totals = $767.62       $857.2732   $857.29   $857.30   $857.30