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	$19.68	10.819%	$21.8092	$21.81	$21.80	$21.80
Purchase #2	$39.96	6.682%	$42.6301	$42.63	$42.65	$42.60
Purchase #3	$211.91	13.260%	$240.0093	$240.01	$240.00	$240.00
Purchase #4	$99.98	11.735%	$111.7127	$111.71	$111.70	$111.70
Purchase #5	$138.76	13.474%	$157.4565	$157.46	$157.45	$157.50
Purchase #6	$102.87	5.663%	$108.6955	$108.70	$108.70	$108.70
Purchase #7	$99.57	3.646%	$103.2003	$103.20	$103.20	$103.20
7 purchase totals =	$712.73		$785.5136	$785.52	$785.50	$785.50