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	$27.32	3.572%	$28.2959	$28.30	$28.30	$28.30
Purchase #2	$53.73	10.684%	$59.4705	$59.47	$59.45	$59.50
Purchase #3	$206.54	7.185%	$221.3799	$221.38	$221.40	$221.40
Purchase #4	$63.71	6.493%	$67.8467	$67.85	$67.85	$67.80
Purchase #5	$223.85	12.158%	$251.0657	$251.07	$251.05	$251.10
Purchase #6	$199.79	10.403%	$220.5742	$220.57	$220.55	$220.60
Purchase #7	$127.92	13.379%	$145.0344	$145.03	$145.05	$145.00
7 purchase totals =	$902.86		$993.6673	$993.67	$993.65	$993.70