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	$19.87	9.380%	$21.7338	$21.73	$21.75	$21.70
Purchase #2	$170.48	5.516%	$179.8837	$179.88	$179.90	$179.90
Purchase #3	$16.41	10.328%	$18.1048	$18.10	$18.10	$18.10
Purchase #4	$103.33	8.172%	$111.7741	$111.77	$111.75	$111.80
Purchase #5	$233.35	10.567%	$258.0081	$258.01	$258.00	$258.00
Purchase #6	$69.88	3.268%	$72.1637	$72.16	$72.15	$72.20
Purchase #7	$20.55	9.528%	$22.508	$22.51	$22.50	$22.50
7 purchase totals =	$633.87		$684.1762	$684.16	$684.15	$684.20