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 $154.28   12.711%   $173.8905   $173.89   $173.90   $173.90  
  Purchase #2 $183.32   11.140%   $203.7418   $203.74   $203.75   $203.70  
  Purchase #3 $163.46   11.745%   $182.6584   $182.66   $182.65   $182.70  
  Purchase #4 $55.39   3.691%   $57.4344   $57.43   $57.45   $57.40  
  Purchase #5 $54.99   6.382%   $58.4995   $58.50   $58.50   $58.50  
  Purchase #6 $193.48   12.631%   $217.9185   $217.92   $217.90   $217.90  
  Purchase #7 $129.54   7.195%   $138.8604   $138.86   $138.85   $138.90  
  7 purchase totals = $934.46       $1,033.0035   $1,033.00   $1,033.00   $1,033.00