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	$14.42	6.413%	$15.3448	$15.34	$15.35	$15.30
Purchase #2	$86.95	13.135%	$98.3709	$98.37	$98.35	$98.40
Purchase #3	$230.95	10.665%	$255.5808	$255.58	$255.60	$255.60
Purchase #4	$152.34	4.618%	$159.3751	$159.38	$159.40	$159.40
Purchase #5	$107.44	3.648%	$111.3594	$111.36	$111.35	$111.40
Purchase #6	$137.72	6.680%	$146.9197	$146.92	$146.90	$146.90
Purchase #7	$59.87	3.829%	$62.1624	$62.16	$62.15	$62.20
7 purchase totals =	$789.69		$849.1131	$849.11	$849.10	$849.20