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	$105.67	3.629%	$109.5048	$109.50	$109.50	$109.50
Purchase #2	$218.78	13.822%	$249.0198	$249.02	$249.00	$249.00
Purchase #3	$10.76	4.805%	$11.277	$11.28	$11.30	$11.30
Purchase #4	$176.99	12.233%	$198.6412	$198.64	$198.65	$198.60
Purchase #5	$170.25	13.571%	$193.3546	$193.35	$193.35	$193.40
Purchase #6	$115.32	10.603%	$127.5474	$127.55	$127.55	$127.50
Purchase #7	$100.27	13.861%	$114.1684	$114.17	$114.15	$114.20
7 purchase totals =	$898.04		$1,003.5132	$1,003.51	$1,003.50	$1,003.50