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	$150.78	3.777%	$156.475	$156.48	$156.50	$156.50
Purchase #2	$79.56	6.168%	$84.4673	$84.47	$84.45	$84.50
Purchase #3	$173.31	8.211%	$187.5405	$187.54	$187.55	$187.50
Purchase #4	$33.94	10.104%	$37.3693	$37.37	$37.35	$37.40
Purchase #5	$179.79	7.771%	$193.7615	$193.76	$193.75	$193.80
Purchase #6	$156.50	6.371%	$166.4706	$166.47	$166.45	$166.50
Purchase #7	$30.82	9.613%	$33.7827	$33.78	$33.80	$33.80
7 purchase totals =	$804.70		$859.8669	$859.87	$859.85	$860.00