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 $32.80   8.183%   $35.484   $35.48   $35.50   $35.50  
  Purchase #2 $23.97   10.472%   $26.4801   $26.48   $26.50   $26.50  
  Purchase #3 $68.73   6.163%   $72.9658   $72.97   $72.95   $73.00  
  Purchase #4 $153.73   7.602%   $165.4166   $165.42   $165.40   $165.40  
  Purchase #5 $164.40   11.801%   $183.8008   $183.80   $183.80   $183.80  
  Purchase #6 $25.25   6.709%   $26.944   $26.94   $26.95   $26.90  
  Purchase #7 $114.65   9.723%   $125.7974   $125.80   $125.80   $125.80  
  7 purchase totals = $583.53       $636.8887   $636.89   $636.90   $636.90