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 $248.63   8.488%   $269.7337   $269.73   $269.75   $269.70  
  Purchase #2 $122.40   8.598%   $132.924   $132.92   $132.90   $132.90  
  Purchase #3 $153.81   10.185%   $169.4755   $169.48   $169.50   $169.50  
  Purchase #4 $74.92   12.226%   $84.0797   $84.08   $84.10   $84.10  
  Purchase #5 $241.84   5.708%   $255.6442   $255.64   $255.65   $255.60  
  Purchase #6 $140.34   8.287%   $151.97   $151.97   $151.95   $152.00  
  Purchase #7 $178.39   8.526%   $193.5995   $193.60   $193.60   $193.60  
  7 purchase totals = $1,160.33       $1,257.4266   $1,257.42   $1,257.45   $1,257.40