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	$96.63	6.866%	$103.2646	$103.26	$103.25	$103.30
Purchase #2	$105.58	11.843%	$118.0838	$118.08	$118.10	$118.10
Purchase #3	$24.72	13.668%	$28.0987	$28.10	$28.10	$28.10
Purchase #4	$238.36	12.177%	$267.3851	$267.39	$267.40	$267.40
Purchase #5	$114.36	7.554%	$122.9988	$123.00	$123.00	$123.00
Purchase #6	$153.40	11.148%	$170.501	$170.50	$170.50	$170.50
Purchase #7	$55.89	6.225%	$59.3692	$59.37	$59.35	$59.40
7 purchase totals =	$788.94		$869.7012	$869.70	$869.70	$869.80