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	$14.42	6.761%	$15.3949	$15.39	$15.40	$15.40
Purchase #2	$101.32	10.837%	$112.3	$112.30	$112.30	$112.30
Purchase #3	$156.36	4.131%	$162.8192	$162.82	$162.80	$162.80
Purchase #4	$106.43	4.392%	$111.1044	$111.10	$111.10	$111.10
Purchase #5	$136.53	4.106%	$142.1359	$142.14	$142.15	$142.10
Purchase #6	$241.74	5.621%	$255.3282	$255.33	$255.35	$255.30
Purchase #7	$87.73	6.831%	$93.7228	$93.72	$93.70	$93.70
7 purchase totals =	$844.53		$892.8054	$892.80	$892.80	$892.70