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	$18.56	10.794%	$20.5634	$20.56	$20.55	$20.60
Purchase #2	$104.34	5.215%	$109.7813	$109.78	$109.80	$109.80
Purchase #3	$141.52	12.492%	$159.1987	$159.20	$159.20	$159.20
Purchase #4	$110.47	10.858%	$122.4648	$122.46	$122.45	$122.50
Purchase #5	$181.54	7.318%	$194.8251	$194.83	$194.85	$194.80
Purchase #6	$249.78	12.211%	$280.2806	$280.28	$280.30	$280.30
Purchase #7	$163.71	5.819%	$173.2363	$173.24	$173.25	$173.20
7 purchase totals =	$969.92		$1,060.3502	$1,060.35	$1,060.40	$1,060.40