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	$122.42	7.666%	$131.8047	$131.80	$131.80	$131.80
Purchase #2	$158.84	10.177%	$175.0051	$175.01	$175.00	$175.00
Purchase #3	$211.80	12.699%	$238.6965	$238.70	$238.70	$238.70
Purchase #4	$53.96	6.475%	$57.4539	$57.45	$57.45	$57.50
Purchase #5	$190.48	12.810%	$214.8805	$214.88	$214.90	$214.90
Purchase #6	$83.63	7.515%	$89.9148	$89.91	$89.90	$89.90
Purchase #7	$154.35	4.381%	$161.1121	$161.11	$161.10	$161.10
7 purchase totals =	$975.48		$1,068.8676	$1,068.86	$1,068.85	$1,068.90