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	$142.64	12.447%	$160.3944	$160.39	$160.40	$160.40
Purchase #2	$28.25	3.697%	$29.2944	$29.29	$29.30	$29.30
Purchase #3	$185.91	5.535%	$196.2001	$196.20	$196.20	$196.20
Purchase #4	$170.46	13.831%	$194.0363	$194.04	$194.05	$194.00
Purchase #5	$230.32	10.580%	$254.6879	$254.69	$254.70	$254.70
Purchase #6	$49.75	9.330%	$54.3917	$54.39	$54.40	$54.40
Purchase #7	$240.29	3.580%	$248.8924	$248.89	$248.90	$248.90
7 purchase totals =	$1,047.62		$1,137.8972	$1,137.89	$1,137.95	$1,137.90