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 $176.97   13.771%   $201.3405   $201.34   $201.35   $201.30  
  Purchase #2 $58.51   13.418%   $66.3609   $66.36   $66.35   $66.40  
  Purchase #3 $227.86   7.422%   $244.7718   $244.77   $244.75   $244.80  
  Purchase #4 $213.51   10.658%   $236.2659   $236.27   $236.25   $236.30  
  Purchase #5 $250.76   10.858%   $277.9875   $277.99   $278.00   $278.00  
  Purchase #6 $104.35   10.183%   $114.976   $114.98   $115.00   $115.00  
  Purchase #7 $206.56   5.784%   $218.5074   $218.51   $218.50   $218.50  
  7 purchase totals = $1,238.52       $1,360.2100   $1,360.22   $1,360.20   $1,360.30