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	$65.73	11.535%	$73.312	$73.31	$73.30	$73.30
Purchase #2	$109.78	9.632%	$120.354	$120.35	$120.35	$120.40
Purchase #3	$17.37	5.823%	$18.3815	$18.38	$18.40	$18.40
Purchase #4	$76.97	11.385%	$85.733	$85.73	$85.75	$85.70
Purchase #5	$200.93	8.434%	$217.8764	$217.88	$217.90	$217.90
Purchase #6	$39.77	6.385%	$42.3093	$42.31	$42.30	$42.30
Purchase #7	$66.60	6.532%	$70.9503	$70.95	$70.95	$71.00
7 purchase totals =	$577.15		$628.9165	$628.91	$628.95	$629.00