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 $164.41   12.546%   $185.0369   $185.04   $185.05   $185.00  
  Purchase #2 $160.99   13.606%   $182.8943   $182.89   $182.90   $182.90  
  Purchase #3 $179.41   6.228%   $190.5837   $190.58   $190.60   $190.60  
  Purchase #4 $32.42   7.872%   $34.9721   $34.97   $34.95   $35.00  
  Purchase #5 $212.26   3.473%   $219.6318   $219.63   $219.65   $219.60  
  Purchase #6 $162.68   12.673%   $183.2964   $183.30   $183.30   $183.30  
  Purchase #7 $154.73   6.156%   $164.2552   $164.26   $164.25   $164.30  
  7 purchase totals = $1,066.90       $1,160.6704   $1,160.67   $1,160.70   $1,160.70