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	$136.32	7.670%	$146.7757	$146.78	$146.80	$146.80
Purchase #2	$34.73	10.659%	$38.4319	$38.43	$38.45	$38.40
Purchase #3	$193.46	6.432%	$205.9033	$205.90	$205.90	$205.90
Purchase #4	$194.33	13.614%	$220.7861	$220.79	$220.80	$220.80
Purchase #5	$159.39	8.476%	$172.8999	$172.90	$172.90	$172.90
Purchase #6	$200.48	3.419%	$207.3344	$207.33	$207.35	$207.30
Purchase #7	$176.90	11.242%	$196.7871	$196.79	$196.80	$196.80
7 purchase totals =	$1,095.61		$1,188.9184	$1,188.92	$1,189.00	$1,188.90