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	$205.89	10.747%	$228.017	$228.02	$228.00	$228.00
Purchase #2	$140.44	4.836%	$147.2317	$147.23	$147.25	$147.20
Purchase #3	$197.59	6.690%	$210.8088	$210.81	$210.80	$210.80
Purchase #4	$34.59	11.576%	$38.5941	$38.59	$38.60	$38.60
Purchase #5	$197.49	5.830%	$209.0037	$209.00	$209.00	$209.00
Purchase #6	$179.38	3.392%	$185.4646	$185.46	$185.45	$185.50
Purchase #7	$228.58	11.768%	$255.4793	$255.48	$255.50	$255.50
7 purchase totals =	$1,183.96		$1,274.5992	$1,274.59	$1,274.60	$1,274.60