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	$67.65	5.157%	$71.1387	$71.14	$71.15	$71.10
Purchase #2	$107.98	10.860%	$119.7066	$119.71	$119.70	$119.70
Purchase #3	$188.72	3.107%	$194.5835	$194.58	$194.60	$194.60
Purchase #4	$57.72	11.513%	$64.3653	$64.37	$64.35	$64.40
Purchase #5	$131.59	9.749%	$144.4187	$144.42	$144.40	$144.40
Purchase #6	$6.75	4.502%	$7.0539	$7.05	$7.05	$7.10
Purchase #7	$56.98	13.341%	$64.5817	$64.58	$64.60	$64.60
7 purchase totals =	$617.39		$665.8484	$665.85	$665.85	$665.90