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	$29.31	9.705%	$32.1545	$32.15	$32.15	$32.20
Purchase #2	$31.29	3.420%	$32.3601	$32.36	$32.35	$32.40
Purchase #3	$66.37	13.595%	$75.393	$75.39	$75.40	$75.40
Purchase #4	$229.59	9.667%	$251.7845	$251.78	$251.80	$251.80
Purchase #5	$99.89	3.169%	$103.0555	$103.06	$103.05	$103.10
Purchase #6	$159.81	13.182%	$180.8762	$180.88	$180.90	$180.90
Purchase #7	$105.31	6.242%	$111.8835	$111.88	$111.90	$111.90
7 purchase totals =	$721.57		$787.5073	$787.50	$787.55	$787.70