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 $26.96   9.508%   $29.5234   $29.52   $29.50   $29.50  
  Purchase #2 $215.31   8.338%   $233.2625   $233.26   $233.25   $233.30  
  Purchase #3 $108.63   3.353%   $112.2724   $112.27   $112.25   $112.30  
  Purchase #4 $210.33   8.186%   $227.5476   $227.55   $227.55   $227.50  
  Purchase #5 $187.71   8.552%   $203.763   $203.76   $203.75   $203.80  
  Purchase #6 $219.94   6.327%   $233.8556   $233.86   $233.85   $233.90  
  Purchase #7 $157.28   12.144%   $176.3801   $176.38   $176.40   $176.40  
  7 purchase totals = $1,126.16       $1,216.6046   $1,216.60   $1,216.55   $1,216.70