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	$70.77	11.816%	$79.1322	$79.13	$79.15	$79.10
Purchase #2	$151.32	13.772%	$172.1598	$172.16	$172.15	$172.20
Purchase #3	$112.35	9.825%	$123.3884	$123.39	$123.40	$123.40
Purchase #4	$121.99	12.823%	$137.6328	$137.63	$137.65	$137.60
Purchase #5	$207.74	5.295%	$218.7398	$218.74	$218.75	$218.70
Purchase #6	$122.65	4.401%	$128.0478	$128.05	$128.05	$128.00
Purchase #7	$85.52	5.507%	$90.2296	$90.23	$90.25	$90.20
7 purchase totals =	$872.34		$949.3304	$949.33	$949.40	$949.20