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	$108.26	13.640%	$123.0267	$123.03	$123.05	$123.00
Purchase #2	$134.66	7.175%	$144.3219	$144.32	$144.30	$144.30
Purchase #3	$9.85	12.854%	$11.1161	$11.12	$11.10	$11.10
Purchase #4	$149.86	4.404%	$156.4598	$156.46	$156.45	$156.50
Purchase #5	$63.55	12.274%	$71.3501	$71.35	$71.35	$71.40
Purchase #6	$141.46	7.598%	$152.2081	$152.21	$152.20	$152.20
Purchase #7	$142.40	10.222%	$156.9561	$156.96	$156.95	$157.00
7 purchase totals =	$750.04		$815.4388	$815.45	$815.40	$815.50