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	$47.32	10.846%	$52.4523	$52.45	$52.45	$52.50
Purchase #2	$97.82	6.633%	$104.3084	$104.31	$104.30	$104.30
Purchase #3	$134.53	5.158%	$141.4691	$141.47	$141.45	$141.50
Purchase #4	$27.87	13.565%	$31.6506	$31.65	$31.65	$31.70
Purchase #5	$29.77	4.668%	$31.1597	$31.16	$31.15	$31.20
Purchase #6	$11.34	9.419%	$12.4081	$12.41	$12.40	$12.40
Purchase #7	$237.39	11.261%	$264.1225	$264.12	$264.10	$264.10
7 purchase totals =	$586.04		$637.5707	$637.57	$637.50	$637.70