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	$20.70	3.110%	$21.3438	$21.34	$21.35	$21.30
Purchase #2	$229.42	10.408%	$253.298	$253.30	$253.30	$253.30
Purchase #3	$120.48	10.545%	$133.1846	$133.18	$133.20	$133.20
Purchase #4	$39.89	6.158%	$42.3464	$42.35	$42.35	$42.30
Purchase #5	$200.32	12.318%	$224.9954	$225.00	$225.00	$225.00
Purchase #6	$63.37	4.869%	$66.4555	$66.46	$66.45	$66.50
Purchase #7	$60.75	11.705%	$67.8608	$67.86	$67.85	$67.90
7 purchase totals =	$734.93		$809.4845	$809.49	$809.50	$809.50