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	$20.28	7.839%	$21.8697	$21.87	$21.85	$21.90
Purchase #2	$197.45	4.779%	$206.8861	$206.89	$206.90	$206.90
Purchase #3	$191.75	13.269%	$217.1933	$217.19	$217.20	$217.20
Purchase #4	$159.39	3.164%	$164.4331	$164.43	$164.45	$164.40
Purchase #5	$46.49	6.278%	$49.4086	$49.41	$49.40	$49.40
Purchase #6	$160.26	6.412%	$170.5359	$170.54	$170.55	$170.50
Purchase #7	$161.94	6.587%	$172.607	$172.61	$172.60	$172.60
7 purchase totals =	$937.56		$1,002.9337	$1,002.94	$1,002.95	$1,002.90