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	$177.72	5.430%	$187.3702	$187.37	$187.35	$187.40
Purchase #2	$120.56	6.401%	$128.277	$128.28	$128.30	$128.30
Purchase #3	$70.50	9.514%	$77.2074	$77.21	$77.20	$77.20
Purchase #4	$180.49	10.231%	$198.9559	$198.96	$198.95	$199.00
Purchase #5	$89.89	11.326%	$100.0709	$100.07	$100.05	$100.10
Purchase #6	$32.95	7.505%	$35.4229	$35.42	$35.40	$35.40
Purchase #7	$42.84	8.453%	$46.4613	$46.46	$46.45	$46.50
7 purchase totals =	$714.95		$773.7656	$773.77	$773.70	$773.90