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 $188.44   11.723%   $210.5308   $210.53   $210.55   $210.50  
  Purchase #2 $218.63   13.631%   $248.4315   $248.43   $248.45   $248.40  
  Purchase #3 $58.69   6.658%   $62.5976   $62.60   $62.60   $62.60  
  Purchase #4 $136.71   7.344%   $146.75   $146.75   $146.75   $146.80  
  Purchase #5 $29.48   6.551%   $31.4112   $31.41   $31.40   $31.40  
  Purchase #6 $164.50   4.730%   $172.2809   $172.28   $172.30   $172.30  
  Purchase #7 $89.79   4.106%   $93.4768   $93.48   $93.50   $93.50  
  7 purchase totals = $886.24       $965.4788   $965.48   $965.55   $965.50