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 $108.55   4.203%   $113.1124   $113.11   $113.10   $113.10  
  Purchase #2 $172.34   11.622%   $192.3694   $192.37   $192.35   $192.40  
  Purchase #3 $182.35   6.121%   $193.5116   $193.51   $193.50   $193.50  
  Purchase #4 $209.78   4.636%   $219.5054   $219.51   $219.50   $219.50  
  Purchase #5 $210.32   5.223%   $221.305   $221.31   $221.30   $221.30  
  Purchase #6 $32.44   8.354%   $35.15   $35.15   $35.15   $35.20  
  Purchase #7 $26.61   6.267%   $28.2776   $28.28   $28.30   $28.30  
  7 purchase totals = $942.39       $1,003.2314   $1,003.24   $1,003.20   $1,003.30