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	$157.67	4.404%	$164.6138	$164.61	$164.60	$164.60
Purchase #2	$17.52	7.513%	$18.8363	$18.84	$18.85	$18.80
Purchase #3	$125.30	11.530%	$139.7471	$139.75	$139.75	$139.70
Purchase #4	$179.71	5.117%	$188.9058	$188.91	$188.90	$188.90
Purchase #5	$107.43	8.205%	$116.2446	$116.24	$116.25	$116.20
Purchase #6	$246.99	9.264%	$269.8712	$269.87	$269.85	$269.90
Purchase #7	$167.71	13.330%	$190.0657	$190.07	$190.05	$190.10
7 purchase totals =	$1,002.33		$1,088.2845	$1,088.29	$1,088.25	$1,088.20