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 $245.86   3.697%   $254.9494   $254.95   $254.95   $254.90  
  Purchase #2 $130.98   4.412%   $136.7588   $136.76   $136.75   $136.80  
  Purchase #3 $118.42   12.226%   $132.898   $132.90   $132.90   $132.90  
  Purchase #4 $191.45   3.755%   $198.6389   $198.64   $198.65   $198.60  
  Purchase #5 $21.75   9.863%   $23.8952   $23.90   $23.90   $23.90  
  Purchase #6 $214.79   11.607%   $239.7207   $239.72   $239.70   $239.70  
  Purchase #7 $187.96   4.294%   $196.031   $196.03   $196.05   $196.00  
  7 purchase totals = $1,111.21       $1,182.8920   $1,182.90   $1,182.90   $1,182.80