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	$150.31	3.710%	$155.8865	$155.89	$155.90	$155.90
Purchase #2	$50.48	11.853%	$56.4634	$56.46	$56.45	$56.50
Purchase #3	$128.90	11.308%	$143.476	$143.48	$143.50	$143.50
Purchase #4	$166.26	10.525%	$183.7589	$183.76	$183.75	$183.80
Purchase #5	$181.74	6.407%	$193.3841	$193.38	$193.40	$193.40
Purchase #6	$152.79	13.433%	$173.3143	$173.31	$173.30	$173.30
Purchase #7	$171.81	13.111%	$194.336	$194.34	$194.35	$194.30
7 purchase totals =	$1,002.29		$1,100.6192	$1,100.62	$1,100.65	$1,100.70