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	$134.90	8.745%	$146.697	$146.70	$146.70	$146.70
Purchase #2	$128.80	6.480%	$137.1462	$137.15	$137.15	$137.10
Purchase #3	$69.55	5.511%	$73.3829	$73.38	$73.40	$73.40
Purchase #4	$241.75	11.465%	$269.4666	$269.47	$269.45	$269.50
Purchase #5	$57.49	4.234%	$59.9241	$59.92	$59.90	$59.90
Purchase #6	$59.47	10.513%	$65.7221	$65.72	$65.70	$65.70
Purchase #7	$43.58	3.462%	$45.0887	$45.09	$45.10	$45.10
7 purchase totals =	$735.54		$797.4276	$797.43	$797.40	$797.40