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	$230.55	10.133%	$253.9116	$253.91	$253.90	$253.90
Purchase #2	$94.49	4.817%	$99.0416	$99.04	$99.05	$99.00
Purchase #3	$54.82	9.808%	$60.1967	$60.20	$60.20	$60.20
Purchase #4	$40.81	12.271%	$45.8178	$45.82	$45.80	$45.80
Purchase #5	$101.86	7.137%	$109.1297	$109.13	$109.15	$109.10
Purchase #6	$177.38	3.298%	$183.23	$183.23	$183.25	$183.20
Purchase #7	$141.75	7.172%	$151.9163	$151.92	$151.90	$151.90
7 purchase totals =	$841.66		$903.2437	$903.25	$903.25	$903.10