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	$73.98	6.128%	$78.5135	$78.51	$78.50	$78.50
Purchase #2	$26.90	9.500%	$29.4555	$29.46	$29.45	$29.50
Purchase #3	$187.52	11.512%	$209.1073	$209.11	$209.10	$209.10
Purchase #4	$25.44	12.103%	$28.519	$28.52	$28.50	$28.50
Purchase #5	$230.29	7.193%	$246.8548	$246.85	$246.85	$246.90
Purchase #6	$68.87	5.152%	$72.4182	$72.42	$72.40	$72.40
Purchase #7	$131.34	11.801%	$146.8394	$146.84	$146.85	$146.80
7 purchase totals =	$744.34		$811.7077	$811.71	$811.65	$811.70