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	$145.52	10.295%	$160.5013	$160.50	$160.50	$160.50
Purchase #2	$92.89	7.832%	$100.1651	$100.17	$100.15	$100.20
Purchase #3	$72.37	9.813%	$79.4717	$79.47	$79.45	$79.50
Purchase #4	$94.67	10.601%	$104.706	$104.71	$104.70	$104.70
Purchase #5	$191.79	3.814%	$199.1049	$199.10	$199.10	$199.10
Purchase #6	$17.93	12.203%	$20.118	$20.12	$20.10	$20.10
Purchase #7	$185.68	5.640%	$196.1524	$196.15	$196.15	$196.20
7 purchase totals =	$800.85		$860.2194	$860.22	$860.15	$860.30