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	$72.39	10.654%	$80.1024	$80.10	$80.10	$80.10
Purchase #2	$152.87	8.465%	$165.8104	$165.81	$165.80	$165.80
Purchase #3	$240.53	6.325%	$255.7435	$255.74	$255.75	$255.70
Purchase #4	$158.82	10.516%	$175.5215	$175.52	$175.50	$175.50
Purchase #5	$96.85	11.351%	$107.8434	$107.84	$107.85	$107.80
Purchase #6	$245.72	13.210%	$278.1796	$278.18	$278.20	$278.20
Purchase #7	$154.28	7.836%	$166.3694	$166.37	$166.35	$166.40
7 purchase totals =	$1,121.46		$1,229.5702	$1,229.56	$1,229.55	$1,229.50