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	$76.35	3.496%	$79.0192	$79.02	$79.00	$79.00
Purchase #2	$41.31	4.867%	$43.3206	$43.32	$43.30	$43.30
Purchase #3	$150.56	6.297%	$160.0408	$160.04	$160.05	$160.00
Purchase #4	$204.62	11.629%	$228.4153	$228.42	$228.40	$228.40
Purchase #5	$85.87	4.554%	$89.7805	$89.78	$89.80	$89.80
Purchase #6	$247.67	5.103%	$260.3086	$260.31	$260.30	$260.30
Purchase #7	$237.87	6.800%	$254.0452	$254.05	$254.05	$254.00
7 purchase totals =	$1,044.25		$1,114.9302	$1,114.94	$1,114.90	$1,114.80