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	$220.56	10.873%	$244.5415	$244.54	$244.55	$244.50
Purchase #2	$59.30	4.115%	$61.7402	$61.74	$61.75	$61.70
Purchase #3	$66.71	5.150%	$70.1456	$70.15	$70.15	$70.10
Purchase #4	$129.50	13.374%	$146.8193	$146.82	$146.80	$146.80
Purchase #5	$129.66	7.788%	$139.7579	$139.76	$139.75	$139.80
Purchase #6	$75.59	6.526%	$80.523	$80.52	$80.50	$80.50
Purchase #7	$148.99	7.140%	$159.6279	$159.63	$159.65	$159.60
7 purchase totals =	$830.31		$903.1554	$903.16	$903.15	$903.00