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	$132.66	10.667%	$146.8108	$146.81	$146.80	$146.80
Purchase #2	$73.28	10.419%	$80.915	$80.92	$80.90	$80.90
Purchase #3	$247.77	5.651%	$261.7715	$261.77	$261.75	$261.80
Purchase #4	$46.52	10.852%	$51.5684	$51.57	$51.55	$51.60
Purchase #5	$130.41	13.549%	$148.0793	$148.08	$148.10	$148.10
Purchase #6	$75.46	9.577%	$82.6868	$82.69	$82.70	$82.70
Purchase #7	$212.40	8.859%	$231.2165	$231.22	$231.20	$231.20
7 purchase totals =	$918.50		$1,003.0483	$1,003.06	$1,003.00	$1,003.10