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	$80.99	12.102%	$90.7914	$90.79	$90.80	$90.80
Purchase #2	$53.25	6.138%	$56.5185	$56.52	$56.50	$56.50
Purchase #3	$207.32	3.428%	$214.4269	$214.43	$214.45	$214.40
Purchase #4	$86.38	12.694%	$97.3451	$97.35	$97.35	$97.30
Purchase #5	$30.98	3.673%	$32.1179	$32.12	$32.10	$32.10
Purchase #6	$90.25	9.514%	$98.8364	$98.84	$98.85	$98.80
Purchase #7	$89.72	11.196%	$99.7651	$99.77	$99.75	$99.80
7 purchase totals =	$638.89		$689.8013	$689.82	$689.80	$689.70