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	$113.26	3.306%	$117.0044	$117.00	$117.00	$117.00
Purchase #2	$109.28	12.631%	$123.0832	$123.08	$123.10	$123.10
Purchase #3	$88.91	13.295%	$100.7306	$100.73	$100.75	$100.70
Purchase #4	$91.35	13.180%	$103.3899	$103.39	$103.40	$103.40
Purchase #5	$60.73	3.847%	$63.0663	$63.07	$63.05	$63.10
Purchase #6	$240.31	11.454%	$267.8351	$267.84	$267.85	$267.80
Purchase #7	$54.61	8.246%	$59.1131	$59.11	$59.10	$59.10
7 purchase totals =	$758.45		$834.2226	$834.22	$834.25	$834.20