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	$250.69	4.303%	$261.4772	$261.48	$261.50	$261.50
Purchase #2	$135.51	13.287%	$153.5152	$153.52	$153.50	$153.50
Purchase #3	$117.91	11.812%	$131.8375	$131.84	$131.85	$131.80
Purchase #4	$124.58	7.192%	$133.5398	$133.54	$133.55	$133.50
Purchase #5	$236.84	9.607%	$259.5932	$259.59	$259.60	$259.60
Purchase #6	$196.39	10.109%	$216.2431	$216.24	$216.25	$216.20
Purchase #7	$51.97	3.847%	$53.9693	$53.97	$53.95	$54.00
7 purchase totals =	$1,113.89		$1,210.1753	$1,210.18	$1,210.20	$1,210.10