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	$205.48	12.298%	$230.7499	$230.75	$230.75	$230.70
Purchase #2	$93.70	3.652%	$97.1219	$97.12	$97.10	$97.10
Purchase #3	$82.52	8.520%	$89.5507	$89.55	$89.55	$89.60
Purchase #4	$126.27	6.405%	$134.3576	$134.36	$134.35	$134.40
Purchase #5	$105.89	6.253%	$112.5113	$112.51	$112.50	$112.50
Purchase #6	$79.74	3.831%	$82.7948	$82.79	$82.80	$82.80
Purchase #7	$146.50	6.777%	$156.4283	$156.43	$156.45	$156.40
7 purchase totals =	$840.10		$903.5145	$903.51	$903.50	$903.50