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	$19.90	3.530%	$20.6025	$20.60	$20.60	$20.60
Purchase #2	$220.38	3.243%	$227.5269	$227.53	$227.55	$227.50
Purchase #3	$108.27	9.542%	$118.6011	$118.60	$118.60	$118.60
Purchase #4	$229.27	13.730%	$260.7488	$260.75	$260.75	$260.70
Purchase #5	$237.63	11.296%	$264.4727	$264.47	$264.45	$264.50
Purchase #6	$247.30	3.637%	$256.2943	$256.29	$256.30	$256.30
Purchase #7	$38.45	12.637%	$43.3089	$43.31	$43.30	$43.30
7 purchase totals =	$1,101.20		$1,191.5552	$1,191.55	$1,191.55	$1,191.50