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	$132.78	10.441%	$146.6436	$146.64	$146.65	$146.60
Purchase #2	$82.73	3.671%	$85.767	$85.77	$85.75	$85.80
Purchase #3	$25.80	8.850%	$28.0833	$28.08	$28.10	$28.10
Purchase #4	$14.51	8.349%	$15.7214	$15.72	$15.70	$15.70
Purchase #5	$180.77	5.286%	$190.3255	$190.33	$190.35	$190.30
Purchase #6	$140.90	3.652%	$146.0457	$146.05	$146.05	$146.00
Purchase #7	$49.72	6.355%	$52.8797	$52.88	$52.90	$52.90
7 purchase totals =	$627.21		$665.4662	$665.47	$665.50	$665.40