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	$25.64	9.873%	$28.1714	$28.17	$28.15	$28.20
Purchase #2	$126.55	9.212%	$138.2078	$138.21	$138.20	$138.20
Purchase #3	$158.71	12.178%	$178.0377	$178.04	$178.05	$178.00
Purchase #4	$57.57	13.298%	$65.2257	$65.23	$65.25	$65.20
Purchase #5	$247.30	6.567%	$263.5402	$263.54	$263.55	$263.50
Purchase #6	$182.52	4.212%	$190.2077	$190.21	$190.20	$190.20
Purchase #7	$127.82	9.231%	$139.6191	$139.62	$139.60	$139.60
7 purchase totals =	$926.11		$1,003.0096	$1,003.02	$1,003.00	$1,002.90