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	$42.54	9.281%	$46.4881	$46.49	$46.50	$46.50
Purchase #2	$219.90	11.704%	$245.6371	$245.64	$245.65	$245.60
Purchase #3	$80.50	13.204%	$91.1292	$91.13	$91.15	$91.10
Purchase #4	$74.78	4.515%	$78.1563	$78.16	$78.15	$78.20
Purchase #5	$93.30	8.167%	$100.9198	$100.92	$100.90	$100.90
Purchase #6	$113.75	6.765%	$121.4452	$121.45	$121.45	$121.40
Purchase #7	$15.31	9.211%	$16.7202	$16.72	$16.70	$16.70
7 purchase totals =	$640.08		$700.4959	$700.51	$700.50	$700.40