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	$238.30	9.364%	$260.6144	$260.61	$260.60	$260.60
Purchase #2	$216.49	6.474%	$230.5056	$230.51	$230.50	$230.50
Purchase #3	$69.45	9.300%	$75.9089	$75.91	$75.90	$75.90
Purchase #4	$166.60	13.671%	$189.3759	$189.38	$189.40	$189.40
Purchase #5	$69.94	12.245%	$78.5042	$78.50	$78.50	$78.50
Purchase #6	$225.80	9.487%	$247.2216	$247.22	$247.20	$247.20
Purchase #7	$85.32	6.413%	$90.7916	$90.79	$90.80	$90.80
7 purchase totals =	$1,071.90		$1,172.9222	$1,172.92	$1,172.90	$1,172.90