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	$42.78	3.223%	$44.1588	$44.16	$44.15	$44.20
Purchase #2	$85.95	7.672%	$92.5441	$92.54	$92.55	$92.50
Purchase #3	$166.74	13.203%	$188.7547	$188.75	$188.75	$188.80
Purchase #4	$40.54	11.408%	$45.1648	$45.16	$45.15	$45.20
Purchase #5	$182.93	4.744%	$191.6082	$191.61	$191.60	$191.60
Purchase #6	$10.67	12.238%	$11.9758	$11.98	$12.00	$12.00
Purchase #7	$250.83	7.350%	$269.266	$269.27	$269.25	$269.30
7 purchase totals =	$780.44		$843.4724	$843.47	$843.45	$843.60