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	$24.40	12.245%	$27.3878	$27.39	$27.40	$27.40
Purchase #2	$135.93	6.272%	$144.4555	$144.46	$144.45	$144.50
Purchase #3	$72.26	4.565%	$75.5587	$75.56	$75.55	$75.60
Purchase #4	$165.43	12.299%	$185.7762	$185.78	$185.80	$185.80
Purchase #5	$47.60	12.416%	$53.51	$53.51	$53.50	$53.50
Purchase #6	$58.54	12.766%	$66.0132	$66.01	$66.00	$66.00
Purchase #7	$133.84	9.761%	$146.9041	$146.90	$146.90	$146.90
7 purchase totals =	$638.00		$699.6055	$699.61	$699.60	$699.70