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	$58.77	9.788%	$64.5224	$64.52	$64.50	$64.50
Purchase #2	$82.68	9.488%	$90.5247	$90.52	$90.50	$90.50
Purchase #3	$166.69	7.761%	$179.6268	$179.63	$179.65	$179.60
Purchase #4	$205.58	7.741%	$221.4939	$221.49	$221.50	$221.50
Purchase #5	$61.99	4.458%	$64.7535	$64.75	$64.75	$64.80
Purchase #6	$121.40	4.841%	$127.277	$127.28	$127.30	$127.30
Purchase #7	$157.42	8.511%	$170.818	$170.82	$170.80	$170.80
7 purchase totals =	$854.53		$919.0163	$919.01	$919.00	$919.00