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 $250.62   12.164%   $281.1054   $281.11   $281.10   $281.10  
  Purchase #2 $147.63   7.452%   $158.6314   $158.63   $158.65   $158.60  
  Purchase #3 $126.29   11.289%   $140.5469   $140.55   $140.55   $140.50  
  Purchase #4 $162.68   8.661%   $176.7697   $176.77   $176.75   $176.80  
  Purchase #5 $53.78   8.376%   $58.2846   $58.28   $58.30   $58.30  
  Purchase #6 $163.38   13.645%   $185.6732   $185.67   $185.65   $185.70  
  Purchase #7 $161.38   4.463%   $168.5824   $168.58   $168.60   $168.60  
  7 purchase totals = $1,065.76       $1,169.5936   $1,169.59   $1,169.60   $1,169.60