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	$50.38	5.754%	$53.2789	$53.28	$53.30	$53.30
Purchase #2	$62.74	13.491%	$71.2043	$71.20	$71.20	$71.20
Purchase #3	$243.43	9.276%	$266.0106	$266.01	$266.00	$266.00
Purchase #4	$54.96	5.283%	$57.8635	$57.86	$57.85	$57.90
Purchase #5	$174.55	5.654%	$184.4191	$184.42	$184.40	$184.40
Purchase #6	$125.45	12.824%	$141.5377	$141.54	$141.55	$141.50
Purchase #7	$25.71	8.165%	$27.8092	$27.81	$27.80	$27.80
7 purchase totals =	$737.22		$802.1233	$802.12	$802.10	$802.10