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	$132.61	5.491%	$139.8916	$139.89	$139.90	$139.90
Purchase #2	$59.70	5.658%	$63.0778	$63.08	$63.10	$63.10
Purchase #3	$89.91	13.260%	$101.8321	$101.83	$101.85	$101.80
Purchase #4	$211.73	13.579%	$240.4808	$240.48	$240.50	$240.50
Purchase #5	$27.30	9.131%	$29.7928	$29.79	$29.80	$29.80
Purchase #6	$216.25	5.628%	$228.4206	$228.42	$228.40	$228.40
Purchase #7	$19.89	13.229%	$22.5212	$22.52	$22.50	$22.50
7 purchase totals =	$757.39		$826.0169	$826.01	$826.05	$826.00