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	$132.39	10.638%	$146.4736	$146.47	$146.45	$146.50
Purchase #2	$42.97	9.187%	$46.9177	$46.92	$46.90	$46.90
Purchase #3	$164.61	3.286%	$170.0191	$170.02	$170.00	$170.00
Purchase #4	$103.71	10.420%	$114.5166	$114.52	$114.50	$114.50
Purchase #5	$149.63	3.766%	$155.2651	$155.27	$155.25	$155.30
Purchase #6	$189.31	5.262%	$199.2715	$199.27	$199.25	$199.30
Purchase #7	$168.98	11.537%	$188.4752	$188.48	$188.50	$188.50
7 purchase totals =	$951.60		$1,020.9388	$1,020.95	$1,020.85	$1,021.00