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	$153.97	4.244%	$160.5045	$160.50	$160.50	$160.50
Purchase #2	$193.53	8.519%	$210.0168	$210.02	$210.00	$210.00
Purchase #3	$156.61	6.586%	$166.9243	$166.92	$166.90	$166.90
Purchase #4	$90.72	9.607%	$99.4355	$99.44	$99.45	$99.40
Purchase #5	$45.34	10.747%	$50.2127	$50.21	$50.20	$50.20
Purchase #6	$236.86	4.350%	$247.1634	$247.16	$247.15	$247.20
Purchase #7	$145.73	7.312%	$156.3858	$156.39	$156.40	$156.40
7 purchase totals =	$1,022.76		$1,090.6430	$1,090.64	$1,090.60	$1,090.60