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	$223.90	6.494%	$238.4401	$238.44	$238.45	$238.40
Purchase #2	$117.52	9.721%	$128.9441	$128.94	$128.95	$128.90
Purchase #3	$116.95	10.250%	$128.9374	$128.94	$128.95	$128.90
Purchase #4	$234.88	9.213%	$256.5195	$256.52	$256.50	$256.50
Purchase #5	$138.44	9.501%	$151.5932	$151.59	$151.60	$151.60
Purchase #6	$88.65	11.306%	$98.6728	$98.67	$98.65	$98.70
Purchase #7	$13.44	7.222%	$14.4106	$14.41	$14.40	$14.40
7 purchase totals =	$933.78		$1,017.5177	$1,017.51	$1,017.50	$1,017.40