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	$137.49	6.433%	$146.3347	$146.33	$146.35	$146.30
Purchase #2	$37.37	3.745%	$38.7695	$38.77	$38.75	$38.80
Purchase #3	$12.99	6.681%	$13.8579	$13.86	$13.85	$13.90
Purchase #4	$138.32	11.341%	$154.0069	$154.01	$154.00	$154.00
Purchase #5	$37.72	4.377%	$39.371	$39.37	$39.35	$39.40
Purchase #6	$89.57	5.377%	$94.3862	$94.39	$94.40	$94.40
Purchase #7	$183.69	4.265%	$191.5244	$191.52	$191.50	$191.50
7 purchase totals =	$637.15		$678.2506	$678.25	$678.20	$678.30