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	$249.61	10.494%	$275.8041	$275.80	$275.80	$275.80
Purchase #2	$59.66	11.325%	$66.4165	$66.42	$66.40	$66.40
Purchase #3	$33.76	12.396%	$37.9449	$37.94	$37.95	$37.90
Purchase #4	$5.76	10.767%	$6.3802	$6.38	$6.40	$6.40
Purchase #5	$104.74	9.333%	$114.5154	$114.52	$114.50	$114.50
Purchase #6	$197.31	7.371%	$211.8537	$211.85	$211.85	$211.90
Purchase #7	$28.39	11.348%	$31.6117	$31.61	$31.60	$31.60
7 purchase totals =	$679.23		$744.5265	$744.52	$744.50	$744.50