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	$31.79	5.245%	$33.4574	$33.46	$33.45	$33.50
Purchase #2	$138.46	10.657%	$153.2157	$153.22	$153.20	$153.20
Purchase #3	$220.81	8.134%	$238.7707	$238.77	$238.75	$238.80
Purchase #4	$239.41	12.175%	$268.5582	$268.56	$268.55	$268.60
Purchase #5	$112.30	13.170%	$127.0899	$127.09	$127.10	$127.10
Purchase #6	$6.69	11.114%	$7.4335	$7.43	$7.45	$7.40
Purchase #7	$153.86	7.504%	$165.4057	$165.41	$165.40	$165.40
7 purchase totals =	$903.32		$993.9311	$993.94	$993.90	$994.00