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	$165.86	6.820%	$177.1717	$177.17	$177.15	$177.20
Purchase #2	$68.49	8.796%	$74.5144	$74.51	$74.50	$74.50
Purchase #3	$85.48	4.578%	$89.3933	$89.39	$89.40	$89.40
Purchase #4	$56.86	7.537%	$61.1455	$61.15	$61.15	$61.10
Purchase #5	$174.74	11.758%	$195.2859	$195.29	$195.30	$195.30
Purchase #6	$199.78	11.150%	$222.0555	$222.06	$222.05	$222.10
Purchase #7	$52.85	9.289%	$57.7592	$57.76	$57.75	$57.80
7 purchase totals =	$804.06		$877.3255	$877.33	$877.30	$877.40