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	$244.39	9.784%	$268.3011	$268.30	$268.30	$268.30
Purchase #2	$107.41	12.252%	$120.5699	$120.57	$120.55	$120.60
Purchase #3	$220.92	12.376%	$248.2611	$248.26	$248.25	$248.30
Purchase #4	$161.69	4.285%	$168.6184	$168.62	$168.60	$168.60
Purchase #5	$247.72	3.633%	$256.7197	$256.72	$256.70	$256.70
Purchase #6	$34.27	9.110%	$37.392	$37.39	$37.40	$37.40
Purchase #7	$52.38	13.457%	$59.4288	$59.43	$59.45	$59.40
7 purchase totals =	$1,068.78		$1,159.2910	$1,159.29	$1,159.25	$1,159.30