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	$51.39	3.634%	$53.2575	$53.26	$53.25	$53.30
Purchase #2	$142.33	7.465%	$152.9549	$152.95	$152.95	$153.00
Purchase #3	$88.78	11.408%	$98.908	$98.91	$98.90	$98.90
Purchase #4	$159.66	13.692%	$181.5206	$181.52	$181.50	$181.50
Purchase #5	$31.64	4.836%	$33.1701	$33.17	$33.15	$33.20
Purchase #6	$24.45	9.569%	$26.7896	$26.79	$26.80	$26.80
Purchase #7	$68.39	5.644%	$72.2499	$72.25	$72.25	$72.20
7 purchase totals =	$566.64		$618.8506	$618.85	$618.80	$618.90