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	$85.68	5.427%	$90.3299	$90.33	$90.35	$90.30
Purchase #2	$230.61	3.169%	$237.918	$237.92	$237.90	$237.90
Purchase #3	$100.84	10.455%	$111.3828	$111.38	$111.40	$111.40
Purchase #4	$86.26	3.417%	$89.2075	$89.21	$89.20	$89.20
Purchase #5	$232.73	6.559%	$247.9948	$247.99	$248.00	$248.00
Purchase #6	$103.87	6.370%	$110.4865	$110.49	$110.50	$110.50
Purchase #7	$19.97	7.485%	$21.4648	$21.46	$21.45	$21.50
7 purchase totals =	$859.96		$908.7843	$908.78	$908.80	$908.80