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 $209.81   8.211%   $227.0375   $227.04   $227.05   $227.00  
  Purchase #2 $173.30   13.601%   $196.8705   $196.87   $196.85   $196.90  
  Purchase #3 $155.96   5.456%   $164.4692   $164.47   $164.45   $164.50  
  Purchase #4 $78.98   8.444%   $85.6491   $85.65   $85.65   $85.60  
  Purchase #5 $176.97   5.641%   $186.9529   $186.95   $186.95   $187.00  
  Purchase #6 $20.60   10.814%   $22.8277   $22.83   $22.85   $22.80  
  Purchase #7 $158.63   4.140%   $165.1973   $165.20   $165.20   $165.20  
  7 purchase totals = $974.25       $1,049.0042   $1,049.01   $1,049.00   $1,049.00