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	$80.70	10.631%	$89.2792	$89.28	$89.30	$89.30
Purchase #2	$129.57	10.313%	$142.9326	$142.93	$142.95	$142.90
Purchase #3	$10.33	10.107%	$11.3741	$11.37	$11.35	$11.40
Purchase #4	$75.45	12.738%	$85.0608	$85.06	$85.05	$85.10
Purchase #5	$139.82	10.115%	$153.9628	$153.96	$153.95	$154.00
Purchase #6	$141.85	7.712%	$152.7895	$152.79	$152.80	$152.80
Purchase #7	$224.31	4.722%	$234.9019	$234.90	$234.90	$234.90
7 purchase totals =	$802.03		$870.3009	$870.29	$870.30	$870.40