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	$169.83	12.244%	$190.624	$190.62	$190.60	$190.60
Purchase #2	$211.81	7.399%	$227.4818	$227.48	$227.50	$227.50
Purchase #3	$53.87	9.106%	$58.7754	$58.78	$58.80	$58.80
Purchase #4	$123.75	11.416%	$137.8773	$137.88	$137.90	$137.90
Purchase #5	$93.45	6.581%	$99.5999	$99.60	$99.60	$99.60
Purchase #6	$75.94	5.236%	$79.9162	$79.92	$79.90	$79.90
Purchase #7	$179.77	5.812%	$190.2182	$190.22	$190.20	$190.20
7 purchase totals =	$908.42		$984.4928	$984.50	$984.50	$984.50