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	$53.30	11.419%	$59.3863	$59.39	$59.40	$59.40
Purchase #2	$152.89	5.117%	$160.7134	$160.71	$160.70	$160.70
Purchase #3	$38.55	3.837%	$40.0292	$40.03	$40.05	$40.00
Purchase #4	$130.98	10.293%	$144.4618	$144.46	$144.45	$144.50
Purchase #5	$190.26	5.415%	$200.5626	$200.56	$200.55	$200.60
Purchase #6	$32.55	5.141%	$34.2234	$34.22	$34.20	$34.20
Purchase #7	$101.89	5.532%	$107.5266	$107.53	$107.55	$107.50
7 purchase totals =	$700.42		$746.9033	$746.90	$746.90	$746.90