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	$82.97	7.803%	$89.4441	$89.44	$89.45	$89.40
Purchase #2	$56.89	3.393%	$58.8203	$58.82	$58.80	$58.80
Purchase #3	$101.85	13.732%	$115.836	$115.84	$115.85	$115.80
Purchase #4	$34.34	4.547%	$35.9014	$35.90	$35.90	$35.90
Purchase #5	$148.30	4.294%	$154.668	$154.67	$154.65	$154.70
Purchase #6	$100.83	10.114%	$111.0279	$111.03	$111.05	$111.00
Purchase #7	$100.34	6.331%	$106.6925	$106.69	$106.70	$106.70
7 purchase totals =	$625.52		$672.3902	$672.39	$672.40	$672.30