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	$174.57	10.838%	$193.4899	$193.49	$193.50	$193.50
Purchase #2	$145.80	6.306%	$154.9941	$154.99	$155.00	$155.00
Purchase #3	$106.83	4.191%	$111.3072	$111.31	$111.30	$111.30
Purchase #4	$28.96	4.787%	$30.3463	$30.35	$30.35	$30.30
Purchase #5	$11.72	11.440%	$13.0608	$13.06	$13.05	$13.10
Purchase #6	$114.74	6.792%	$122.5331	$122.53	$122.55	$122.50
Purchase #7	$37.70	10.334%	$41.5959	$41.60	$41.60	$41.60
7 purchase totals =	$620.32		$667.3273	$667.33	$667.35	$667.30