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	$218.36	12.384%	$245.4017	$245.40	$245.40	$245.40
Purchase #2	$65.45	11.419%	$72.9237	$72.92	$72.90	$72.90
Purchase #3	$174.66	9.358%	$191.0047	$191.00	$191.00	$191.00
Purchase #4	$61.99	13.547%	$70.3878	$70.39	$70.40	$70.40
Purchase #5	$156.86	5.348%	$165.2489	$165.25	$165.25	$165.20
Purchase #6	$9.92	3.487%	$10.2659	$10.27	$10.25	$10.30
Purchase #7	$29.46	7.254%	$31.597	$31.60	$31.60	$31.60
7 purchase totals =	$716.70		$786.8297	$786.83	$786.80	$786.80