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	$246.40	10.641%	$272.6194	$272.62	$272.60	$272.60
Purchase #2	$72.69	12.452%	$81.7414	$81.74	$81.75	$81.70
Purchase #3	$159.79	5.847%	$169.1329	$169.13	$169.15	$169.10
Purchase #4	$20.91	3.224%	$21.5841	$21.58	$21.60	$21.60
Purchase #5	$89.89	11.823%	$100.5177	$100.52	$100.50	$100.50
Purchase #6	$134.28	12.155%	$150.6017	$150.60	$150.60	$150.60
Purchase #7	$50.96	10.600%	$56.3618	$56.36	$56.35	$56.40
7 purchase totals =	$774.92		$852.5590	$852.55	$852.55	$852.50