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	$89.39	12.848%	$100.8748	$100.87	$100.85	$100.90
Purchase #2	$156.46	3.671%	$162.2036	$162.20	$162.20	$162.20
Purchase #3	$146.99	3.214%	$151.7143	$151.71	$151.70	$151.70
Purchase #4	$150.39	6.653%	$160.3954	$160.40	$160.40	$160.40
Purchase #5	$152.50	3.677%	$158.1074	$158.11	$158.10	$158.10
Purchase #6	$30.65	10.501%	$33.8686	$33.87	$33.85	$33.90
Purchase #7	$144.32	5.544%	$152.3211	$152.32	$152.30	$152.30
7 purchase totals =	$870.70		$919.4852	$919.48	$919.40	$919.50