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	$92.49	7.223%	$99.1706	$99.17	$99.15	$99.20
Purchase #2	$51.29	13.323%	$58.1234	$58.12	$58.10	$58.10
Purchase #3	$28.30	12.381%	$31.8038	$31.80	$31.80	$31.80
Purchase #4	$205.72	5.321%	$216.6664	$216.67	$216.65	$216.70
Purchase #5	$95.74	8.291%	$103.6778	$103.68	$103.70	$103.70
Purchase #6	$139.78	13.866%	$159.1619	$159.16	$159.15	$159.20
Purchase #7	$90.61	9.521%	$99.237	$99.24	$99.25	$99.20
7 purchase totals =	$703.93		$767.8409	$767.84	$767.80	$767.90