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	$171.98	5.549%	$181.5232	$181.52	$181.50	$181.50
Purchase #2	$147.34	12.130%	$165.2123	$165.21	$165.20	$165.20
Purchase #3	$19.81	8.567%	$21.5071	$21.51	$21.50	$21.50
Purchase #4	$7.50	5.535%	$7.9151	$7.92	$7.90	$7.90
Purchase #5	$135.83	6.247%	$144.3153	$144.32	$144.30	$144.30
Purchase #6	$36.67	9.108%	$40.0099	$40.01	$40.00	$40.00
Purchase #7	$171.25	11.107%	$190.2707	$190.27	$190.25	$190.30
7 purchase totals =	$690.38		$750.7536	$750.76	$750.65	$750.70