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	$120.96	8.486%	$131.2247	$131.22	$131.20	$131.20
Purchase #2	$235.54	9.285%	$257.4099	$257.41	$257.40	$257.40
Purchase #3	$67.32	6.335%	$71.5847	$71.58	$71.60	$71.60
Purchase #4	$94.52	4.810%	$99.0664	$99.07	$99.05	$99.10
Purchase #5	$176.42	8.742%	$191.8426	$191.84	$191.85	$191.80
Purchase #6	$90.38	3.848%	$93.8578	$93.86	$93.85	$93.90
Purchase #7	$51.40	3.211%	$53.0505	$53.05	$53.05	$53.10
7 purchase totals =	$836.54		$898.0366	$898.03	$898.00	$898.10