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	$109.30	11.827%	$122.2269	$122.23	$122.25	$122.20
Purchase #2	$44.48	9.221%	$48.5815	$48.58	$48.60	$48.60
Purchase #3	$195.39	11.709%	$218.2682	$218.27	$218.25	$218.30
Purchase #4	$53.73	11.474%	$59.895	$59.90	$59.90	$59.90
Purchase #5	$244.40	12.622%	$275.2482	$275.25	$275.25	$275.20
Purchase #6	$109.25	5.280%	$115.0184	$115.02	$115.00	$115.00
Purchase #7	$149.27	7.291%	$160.1533	$160.15	$160.15	$160.20
7 purchase totals =	$905.82		$999.3915	$999.40	$999.40	$999.40