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	$54.55	10.429%	$60.239	$60.24	$60.25	$60.20
Purchase #2	$240.80	8.281%	$260.7406	$260.74	$260.75	$260.70
Purchase #3	$143.40	10.172%	$157.9866	$157.99	$158.00	$158.00
Purchase #4	$28.56	12.372%	$32.0934	$32.09	$32.10	$32.10
Purchase #5	$82.28	9.244%	$89.886	$89.89	$89.90	$89.90
Purchase #6	$235.69	7.804%	$254.0832	$254.08	$254.10	$254.10
Purchase #7	$136.44	8.806%	$148.4549	$148.45	$148.45	$148.50
7 purchase totals =	$921.72		$1,003.4837	$1,003.48	$1,003.55	$1,003.50