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	$25.82	11.609%	$28.8174	$28.82	$28.80	$28.80
Purchase #2	$89.43	7.104%	$95.7831	$95.78	$95.80	$95.80
Purchase #3	$38.92	6.523%	$41.4588	$41.46	$41.45	$41.50
Purchase #4	$105.82	13.619%	$120.2316	$120.23	$120.25	$120.20
Purchase #5	$207.90	13.457%	$235.8771	$235.88	$235.90	$235.90
Purchase #6	$37.38	12.717%	$42.1336	$42.13	$42.15	$42.10
Purchase #7	$171.81	12.429%	$193.1643	$193.16	$193.15	$193.20
7 purchase totals =	$677.08		$757.4659	$757.46	$757.50	$757.50