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	$218.73	9.697%	$239.9402	$239.94	$239.95	$239.90
Purchase #2	$56.65	5.257%	$59.6281	$59.63	$59.65	$59.60
Purchase #3	$102.35	12.138%	$114.7732	$114.77	$114.75	$114.80
Purchase #4	$159.86	3.543%	$165.5238	$165.52	$165.50	$165.50
Purchase #5	$105.87	9.673%	$116.1108	$116.11	$116.10	$116.10
Purchase #6	$28.46	13.191%	$32.2142	$32.21	$32.20	$32.20
Purchase #7	$42.35	10.309%	$46.7159	$46.72	$46.70	$46.70
7 purchase totals =	$714.27		$774.9062	$774.90	$774.85	$774.80