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 $165.48   11.786%   $184.9835   $184.98   $185.00   $185.00  
  Purchase #2 $115.35   3.678%   $119.5926   $119.59   $119.60   $119.60  
  Purchase #3 $124.58   7.151%   $133.4887   $133.49   $133.50   $133.50  
  Purchase #4 $158.77   3.592%   $164.473   $164.47   $164.45   $164.50  
  Purchase #5 $7.91   5.104%   $8.3137   $8.31   $8.30   $8.30  
  Purchase #6 $132.42   13.272%   $149.9948   $149.99   $150.00   $150.00  
  Purchase #7 $23.25   9.871%   $25.545   $25.55   $25.55   $25.50  
  7 purchase totals = $727.76       $786.3913   $786.38   $786.40   $786.40