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	$72.90	8.432%	$79.0469	$79.05	$79.05	$79.00
Purchase #2	$132.50	6.483%	$141.09	$141.09	$141.10	$141.10
Purchase #3	$191.26	4.656%	$200.1651	$200.17	$200.15	$200.20
Purchase #4	$113.45	4.588%	$118.6551	$118.66	$118.65	$118.70
Purchase #5	$169.68	8.508%	$184.1164	$184.12	$184.10	$184.10
Purchase #6	$20.83	3.475%	$21.5538	$21.55	$21.55	$21.60
Purchase #7	$38.41	11.625%	$42.8752	$42.88	$42.90	$42.90
7 purchase totals =	$739.03		$787.5025	$787.52	$787.50	$787.60