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	$235.93	12.106%	$264.4917	$264.49	$264.50	$264.50
Purchase #2	$61.33	6.480%	$65.3042	$65.30	$65.30	$65.30
Purchase #3	$30.94	5.412%	$32.6145	$32.61	$32.60	$32.60
Purchase #4	$41.47	10.553%	$45.8463	$45.85	$45.85	$45.80
Purchase #5	$129.36	5.700%	$136.7335	$136.73	$136.75	$136.70
Purchase #6	$79.40	3.307%	$82.0258	$82.03	$82.05	$82.00
Purchase #7	$134.77	6.744%	$143.8589	$143.86	$143.85	$143.90
7 purchase totals =	$713.20		$770.8749	$770.87	$770.90	$770.80