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 $223.86   13.763%   $254.6699   $254.67   $254.65   $254.70  
  Purchase #2 $98.49   9.309%   $107.6584   $107.66   $107.65   $107.70  
  Purchase #3 $112.87   3.615%   $116.9503   $116.95   $116.95   $117.00  
  Purchase #4 $165.52   10.306%   $182.5785   $182.58   $182.60   $182.60  
  Purchase #5 $152.61   11.306%   $169.8641   $169.86   $169.85   $169.90  
  Purchase #6 $22.87   13.836%   $26.0343   $26.03   $26.05   $26.00  
  Purchase #7 $183.32   6.445%   $195.135   $195.14   $195.15   $195.10  
  7 purchase totals = $959.54       $1,052.8905   $1,052.89   $1,052.90   $1,053.00