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	$90.72	9.211%	$99.0762	$99.08	$99.10	$99.10
Purchase #2	$233.98	11.319%	$260.4642	$260.46	$260.45	$260.50
Purchase #3	$223.72	12.157%	$250.9176	$250.92	$250.90	$250.90
Purchase #4	$22.80	4.768%	$23.8871	$23.89	$23.90	$23.90
Purchase #5	$183.41	6.128%	$194.6494	$194.65	$194.65	$194.60
Purchase #6	$66.37	7.229%	$71.1679	$71.17	$71.15	$71.20
Purchase #7	$43.51	6.701%	$46.4256	$46.43	$46.45	$46.40
7 purchase totals =	$864.51		$946.5880	$946.60	$946.60	$946.60