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 $227.72   8.298%   $246.6162   $246.62   $246.60   $246.60  
  Purchase #2 $234.45   7.649%   $252.3831   $252.38   $252.40   $252.40  
  Purchase #3 $202.43   10.679%   $224.0475   $224.05   $224.05   $224.00  
  Purchase #4 $175.89   4.536%   $183.8684   $183.87   $183.85   $183.90  
  Purchase #5 $215.96   7.301%   $231.7272   $231.73   $231.75   $231.70  
  Purchase #6 $50.63   4.203%   $52.758   $52.76   $52.75   $52.80  
  Purchase #7 $159.51   8.459%   $173.003   $173.00   $173.00   $173.00  
  7 purchase totals = $1,266.59       $1,364.4034   $1,364.41   $1,364.40   $1,364.40