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	$37.34	8.505%	$40.5158	$40.52	$40.50	$40.50
Purchase #2	$122.42	4.111%	$127.4527	$127.45	$127.45	$127.50
Purchase #3	$234.96	10.145%	$258.7967	$258.80	$258.80	$258.80
Purchase #4	$36.25	6.775%	$38.7059	$38.71	$38.70	$38.70
Purchase #5	$195.80	7.543%	$210.5692	$210.57	$210.55	$210.60
Purchase #6	$33.84	4.647%	$35.4125	$35.41	$35.40	$35.40
Purchase #7	$68.31	9.629%	$74.8876	$74.89	$74.90	$74.90
7 purchase totals =	$728.92		$786.3404	$786.35	$786.30	$786.40