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	$93.28	5.511%	$98.4207	$98.42	$98.40	$98.40
Purchase #2	$26.32	10.820%	$29.1678	$29.17	$29.15	$29.20
Purchase #3	$161.56	4.791%	$169.3003	$169.30	$169.30	$169.30
Purchase #4	$17.36	4.164%	$18.0829	$18.08	$18.10	$18.10
Purchase #5	$19.67	9.258%	$21.491	$21.49	$21.50	$21.50
Purchase #6	$184.90	10.781%	$204.8341	$204.83	$204.85	$204.80
Purchase #7	$33.73	11.462%	$37.5961	$37.60	$37.60	$37.60
7 purchase totals =	$536.82		$578.8929	$578.89	$578.90	$578.90