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	$19.56	6.724%	$20.8752	$20.88	$20.90	$20.90
Purchase #2	$191.76	11.450%	$213.7165	$213.72	$213.70	$213.70
Purchase #3	$235.45	13.749%	$267.822	$267.82	$267.80	$267.80
Purchase #4	$238.85	12.834%	$269.504	$269.50	$269.50	$269.50
Purchase #5	$190.87	4.664%	$199.7722	$199.77	$199.75	$199.80
Purchase #6	$201.60	10.231%	$222.2257	$222.23	$222.25	$222.20
Purchase #7	$207.40	10.665%	$229.5192	$229.52	$229.50	$229.50
7 purchase totals =	$1,285.49		$1,423.4348	$1,423.44	$1,423.40	$1,423.40