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	$51.67	3.501%	$53.479	$53.48	$53.50	$53.50
Purchase #2	$79.83	13.415%	$90.5392	$90.54	$90.55	$90.50
Purchase #3	$61.74	3.726%	$64.0404	$64.04	$64.05	$64.00
Purchase #4	$172.63	10.816%	$191.3017	$191.30	$191.30	$191.30
Purchase #5	$74.76	7.705%	$80.5203	$80.52	$80.50	$80.50
Purchase #6	$11.54	8.398%	$12.5091	$12.51	$12.50	$12.50
Purchase #7	$51.45	11.287%	$57.2572	$57.26	$57.25	$57.30
7 purchase totals =	$503.62		$549.6469	$549.65	$549.65	$549.60