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 $24.38   8.136%   $26.3636   $26.36   $26.35   $26.40  
  Purchase #2 $156.26   13.673%   $177.6254   $177.63   $177.65   $177.60  
  Purchase #3 $27.63   6.712%   $29.4845   $29.48   $29.50   $29.50  
  Purchase #4 $208.27   11.155%   $231.5025   $231.50   $231.50   $231.50  
  Purchase #5 $76.62   4.285%   $79.9032   $79.90   $79.90   $79.90  
  Purchase #6 $214.82   8.871%   $233.8767   $233.88   $233.90   $233.90  
  Purchase #7 $234.72   9.427%   $256.8471   $256.85   $256.85   $256.80  
  7 purchase totals = $942.70       $1,035.6030   $1,035.60   $1,035.65   $1,035.60