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 $62.71   10.552%   $69.3272   $69.33   $69.35   $69.30  
  Purchase #2 $248.79   11.828%   $278.2169   $278.22   $278.20   $278.20  
  Purchase #3 $211.84   10.208%   $233.4646   $233.46   $233.45   $233.50  
  Purchase #4 $56.71   12.146%   $63.598   $63.60   $63.60   $63.60  
  Purchase #5 $120.68   10.103%   $132.8723   $132.87   $132.85   $132.90  
  Purchase #6 $195.89   13.644%   $222.6172   $222.62   $222.60   $222.60  
  Purchase #7 $125.77   8.620%   $136.6114   $136.61   $136.60   $136.60  
  7 purchase totals = $1,022.39       $1,136.7076   $1,136.71   $1,136.65   $1,136.70