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	$106.78	4.573%	$111.663	$111.66	$111.65	$111.70
Purchase #2	$170.76	8.306%	$184.9433	$184.94	$184.95	$184.90
Purchase #3	$147.47	12.512%	$165.9214	$165.92	$165.90	$165.90
Purchase #4	$30.63	6.215%	$32.5337	$32.53	$32.55	$32.50
Purchase #5	$97.92	4.482%	$102.3088	$102.31	$102.30	$102.30
Purchase #6	$172.70	8.602%	$187.5557	$187.56	$187.55	$187.60
Purchase #7	$53.32	10.111%	$58.7112	$58.71	$58.70	$58.70
7 purchase totals =	$779.58		$843.6371	$843.63	$843.60	$843.60