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	$109.88	4.586%	$114.9191	$114.92	$114.90	$114.90
Purchase #2	$198.39	13.519%	$225.2103	$225.21	$225.20	$225.20
Purchase #3	$244.78	11.305%	$272.4524	$272.45	$272.45	$272.50
Purchase #4	$115.72	10.321%	$127.6635	$127.66	$127.65	$127.70
Purchase #5	$175.35	5.575%	$185.1258	$185.13	$185.15	$185.10
Purchase #6	$190.93	13.403%	$216.5203	$216.52	$216.50	$216.50
Purchase #7	$117.56	7.585%	$126.4769	$126.48	$126.50	$126.50
7 purchase totals =	$1,152.61		$1,268.3683	$1,268.37	$1,268.35	$1,268.40