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	$141.87	12.488%	$159.5867	$159.59	$159.60	$159.60
Purchase #2	$177.40	12.321%	$199.2575	$199.26	$199.25	$199.30
Purchase #3	$141.66	10.776%	$156.9253	$156.93	$156.95	$156.90
Purchase #4	$148.62	8.229%	$160.8499	$160.85	$160.85	$160.80
Purchase #5	$39.52	4.813%	$41.4221	$41.42	$41.40	$41.40
Purchase #6	$127.30	13.439%	$144.4078	$144.41	$144.40	$144.40
Purchase #7	$176.72	6.514%	$188.2315	$188.23	$188.25	$188.20
7 purchase totals =	$953.09		$1,050.6808	$1,050.69	$1,050.70	$1,050.60