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	$80.49	11.361%	$89.6345	$89.63	$89.65	$89.60
Purchase #2	$120.62	7.139%	$129.2311	$129.23	$129.25	$129.20
Purchase #3	$80.96	10.544%	$89.4964	$89.50	$89.50	$89.50
Purchase #4	$8.80	3.191%	$9.0808	$9.08	$9.10	$9.10
Purchase #5	$74.49	10.791%	$82.5282	$82.53	$82.55	$82.50
Purchase #6	$152.37	10.330%	$168.1098	$168.11	$168.10	$168.10
Purchase #7	$167.70	3.422%	$173.4387	$173.44	$173.45	$173.40
7 purchase totals =	$685.43		$741.5195	$741.52	$741.60	$741.40