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	$165.49	3.627%	$171.4923	$171.49	$171.50	$171.50
Purchase #2	$183.27	8.728%	$199.2658	$199.27	$199.25	$199.30
Purchase #3	$245.76	5.756%	$259.9059	$259.91	$259.90	$259.90
Purchase #4	$173.76	10.123%	$191.3497	$191.35	$191.35	$191.30
Purchase #5	$71.78	12.624%	$80.8415	$80.84	$80.85	$80.80
Purchase #6	$31.85	10.831%	$35.2997	$35.30	$35.30	$35.30
Purchase #7	$244.94	13.350%	$277.6395	$277.64	$277.65	$277.60
7 purchase totals =	$1,116.85		$1,215.7944	$1,215.80	$1,215.80	$1,215.70