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	$39.37	6.398%	$41.8889	$41.89	$41.90	$41.90
Purchase #2	$181.30	10.790%	$200.8623	$200.86	$200.85	$200.90
Purchase #3	$183.61	3.719%	$190.4385	$190.44	$190.45	$190.40
Purchase #4	$122.51	6.688%	$130.7035	$130.70	$130.70	$130.70
Purchase #5	$239.76	3.365%	$247.8279	$247.83	$247.85	$247.80
Purchase #6	$200.63	3.373%	$207.3972	$207.40	$207.40	$207.40
Purchase #7	$139.39	10.191%	$153.5952	$153.60	$153.60	$153.60
7 purchase totals =	$1,106.57		$1,172.7135	$1,172.72	$1,172.75	$1,172.70