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	$14.63	5.824%	$15.4821	$15.48	$15.50	$15.50
Purchase #2	$127.85	13.250%	$144.7901	$144.79	$144.80	$144.80
Purchase #3	$149.30	5.115%	$156.9367	$156.94	$156.95	$156.90
Purchase #4	$15.66	10.308%	$17.2742	$17.27	$17.25	$17.30
Purchase #5	$221.93	7.519%	$238.6169	$238.62	$238.60	$238.60
Purchase #6	$235.43	6.294%	$250.248	$250.25	$250.25	$250.20
Purchase #7	$158.96	5.225%	$167.2657	$167.27	$167.25	$167.30
7 purchase totals =	$923.76		$990.6137	$990.62	$990.60	$990.60