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	$54.97	7.363%	$59.0174	$59.02	$59.00	$59.00
Purchase #2	$212.98	10.258%	$234.8275	$234.83	$234.85	$234.80
Purchase #3	$150.50	3.604%	$155.924	$155.92	$155.90	$155.90
Purchase #4	$46.37	11.109%	$51.5212	$51.52	$51.50	$51.50
Purchase #5	$161.69	3.746%	$167.7469	$167.75	$167.75	$167.70
Purchase #6	$79.26	12.393%	$89.0827	$89.08	$89.10	$89.10
Purchase #7	$52.96	6.833%	$56.5788	$56.58	$56.60	$56.60
7 purchase totals =	$758.73		$814.6985	$814.70	$814.70	$814.60