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	$20.90	5.371%	$22.0225	$22.02	$22.00	$22.00
Purchase #2	$51.66	9.812%	$56.7289	$56.73	$56.75	$56.70
Purchase #3	$121.56	9.799%	$133.4717	$133.47	$133.45	$133.50
Purchase #4	$38.76	5.130%	$40.7484	$40.75	$40.75	$40.70
Purchase #5	$17.31	11.315%	$19.2686	$19.27	$19.25	$19.30
Purchase #6	$80.68	12.249%	$90.5625	$90.56	$90.55	$90.60
Purchase #7	$142.63	6.194%	$151.4645	$151.46	$151.45	$151.50
7 purchase totals =	$473.50		$514.2671	$514.26	$514.20	$514.30