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	$18.28	9.356%	$19.9903	$19.99	$20.00	$20.00
Purchase #2	$98.91	9.808%	$108.6111	$108.61	$108.60	$108.60
Purchase #3	$105.68	5.777%	$111.7851	$111.79	$111.80	$111.80
Purchase #4	$30.51	3.482%	$31.5724	$31.57	$31.55	$31.60
Purchase #5	$79.59	3.463%	$82.3462	$82.35	$82.35	$82.30
Purchase #6	$71.37	13.374%	$80.915	$80.92	$80.90	$80.90
Purchase #7	$159.78	5.839%	$169.1096	$169.11	$169.10	$169.10
7 purchase totals =	$564.12		$604.3297	$604.34	$604.30	$604.30