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	$130.38	9.298%	$142.5027	$142.50	$142.50	$142.50
Purchase #2	$184.73	5.191%	$194.3193	$194.32	$194.30	$194.30
Purchase #3	$197.86	12.362%	$222.3195	$222.32	$222.30	$222.30
Purchase #4	$123.71	4.798%	$129.6456	$129.65	$129.65	$129.60
Purchase #5	$193.65	5.771%	$204.8255	$204.83	$204.85	$204.80
Purchase #6	$68.90	13.868%	$78.4551	$78.46	$78.45	$78.50
Purchase #7	$46.71	3.184%	$48.1972	$48.20	$48.20	$48.20
7 purchase totals =	$945.94		$1,020.2649	$1,020.28	$1,020.25	$1,020.20