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	$126.88	13.650%	$144.1991	$144.20	$144.20	$144.20
Purchase #2	$61.89	6.446%	$65.8794	$65.88	$65.90	$65.90
Purchase #3	$30.92	10.510%	$34.1697	$34.17	$34.15	$34.20
Purchase #4	$169.91	5.298%	$178.9118	$178.91	$178.90	$178.90
Purchase #5	$148.44	12.757%	$167.3765	$167.38	$167.40	$167.40
Purchase #6	$42.50	5.615%	$44.8864	$44.89	$44.90	$44.90
Purchase #7	$151.78	13.118%	$171.6905	$171.69	$171.70	$171.70
7 purchase totals =	$732.32		$807.1134	$807.12	$807.15	$807.20