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 $185.40   13.608%   $210.6292   $210.63   $210.65   $210.60  
  Purchase #2 $25.96   4.212%   $27.0534   $27.05   $27.05   $27.10  
  Purchase #3 $89.69   3.203%   $92.5628   $92.56   $92.55   $92.60  
  Purchase #4 $99.41   10.223%   $109.5727   $109.57   $109.55   $109.60  
  Purchase #5 $167.99   5.763%   $177.6713   $177.67   $177.65   $177.70  
  Purchase #6 $197.64   5.828%   $209.1585   $209.16   $209.15   $209.20  
  Purchase #7 $232.99   4.124%   $242.5985   $242.60   $242.60   $242.60  
  7 purchase totals = $999.08       $1,069.2464   $1,069.24   $1,069.20   $1,069.40