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	$53.74	11.396%	$59.8642	$59.86	$59.85	$59.90
Purchase #2	$136.77	11.687%	$152.7543	$152.75	$152.75	$152.80
Purchase #3	$16.83	5.501%	$17.7558	$17.76	$17.75	$17.80
Purchase #4	$55.41	3.315%	$57.2468	$57.25	$57.25	$57.20
Purchase #5	$101.60	4.742%	$106.4179	$106.42	$106.40	$106.40
Purchase #6	$21.59	7.825%	$23.2794	$23.28	$23.30	$23.30
Purchase #7	$164.55	5.492%	$173.5871	$173.59	$173.60	$173.60
7 purchase totals =	$550.49		$590.9055	$590.91	$590.90	$591.00