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	$138.33	4.753%	$144.9048	$144.90	$144.90	$144.90
Purchase #2	$30.75	6.516%	$32.7537	$32.75	$32.75	$32.80
Purchase #3	$20.60	11.329%	$22.9338	$22.93	$22.95	$22.90
Purchase #4	$81.78	8.266%	$88.5399	$88.54	$88.55	$88.50
Purchase #5	$173.84	5.284%	$183.0257	$183.03	$183.05	$183.00
Purchase #6	$51.75	11.743%	$57.827	$57.83	$57.85	$57.80
Purchase #7	$53.41	10.650%	$59.0982	$59.10	$59.10	$59.10
7 purchase totals =	$550.46		$589.0831	$589.08	$589.15	$589.00