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	$102.87	8.343%	$111.4524	$111.45	$111.45	$111.50
Purchase #2	$26.49	4.692%	$27.7329	$27.73	$27.75	$27.70
Purchase #3	$110.83	13.266%	$125.5327	$125.53	$125.55	$125.50
Purchase #4	$107.75	5.279%	$113.4381	$113.44	$113.45	$113.40
Purchase #5	$110.82	11.103%	$123.1243	$123.12	$123.10	$123.10
Purchase #6	$58.56	11.421%	$65.2481	$65.25	$65.25	$65.20
Purchase #7	$43.73	7.198%	$46.8777	$46.88	$46.90	$46.90
7 purchase totals =	$561.05		$613.4062	$613.40	$613.45	$613.30