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	$33.26	13.662%	$37.804	$37.80	$37.80	$37.80
Purchase #2	$170.81	10.378%	$188.5367	$188.54	$188.55	$188.50
Purchase #3	$50.42	8.303%	$54.6064	$54.61	$54.60	$54.60
Purchase #4	$207.81	11.128%	$230.9351	$230.94	$230.95	$230.90
Purchase #5	$208.69	8.222%	$225.8485	$225.85	$225.85	$225.80
Purchase #6	$20.33	6.781%	$21.7086	$21.71	$21.70	$21.70
Purchase #7	$196.98	13.278%	$223.135	$223.14	$223.15	$223.10
7 purchase totals =	$888.30		$982.5743	$982.59	$982.60	$982.40