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	$31.36	5.327%	$33.0305	$33.03	$33.05	$33.00
Purchase #2	$70.35	12.203%	$78.9348	$78.93	$78.95	$78.90
Purchase #3	$105.53	8.624%	$114.6309	$114.63	$114.65	$114.60
Purchase #4	$82.40	5.518%	$86.9468	$86.95	$86.95	$86.90
Purchase #5	$249.36	13.438%	$282.869	$282.87	$282.85	$282.90
Purchase #6	$36.37	6.726%	$38.8162	$38.82	$38.80	$38.80
Purchase #7	$42.49	13.184%	$48.0919	$48.09	$48.10	$48.10
7 purchase totals =	$617.86		$683.3201	$683.32	$683.35	$683.20