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	$80.58	12.396%	$90.5687	$90.57	$90.55	$90.60
Purchase #2	$105.43	10.817%	$116.8344	$116.83	$116.85	$116.80
Purchase #3	$207.63	9.371%	$227.087	$227.09	$227.10	$227.10
Purchase #4	$244.89	3.848%	$254.3134	$254.31	$254.30	$254.30
Purchase #5	$152.82	7.190%	$163.8078	$163.81	$163.80	$163.80
Purchase #6	$166.67	3.398%	$172.3334	$172.33	$172.35	$172.30
Purchase #7	$157.75	11.360%	$175.6704	$175.67	$175.65	$175.70
7 purchase totals =	$1,115.77		$1,200.6151	$1,200.61	$1,200.60	$1,200.60