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 $218.50   11.854%   $244.401   $244.40   $244.40   $244.40  
  Purchase #2 $115.57   5.369%   $121.775   $121.78   $121.80   $121.80  
  Purchase #3 $113.73   12.269%   $127.6835   $127.68   $127.70   $127.70  
  Purchase #4 $115.85   3.122%   $119.4668   $119.47   $119.45   $119.50  
  Purchase #5 $188.43   10.380%   $207.989   $207.99   $208.00   $208.00  
  Purchase #6 $106.99   4.159%   $111.4397   $111.44   $111.45   $111.40  
  Purchase #7 $145.84   4.212%   $151.9828   $151.98   $152.00   $152.00  
  7 purchase totals = $1,004.91       $1,084.7378   $1,084.74   $1,084.80   $1,084.80