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	$34.29	6.556%	$36.5381	$36.54	$36.55	$36.50
Purchase #2	$211.96	10.177%	$233.5312	$233.53	$233.55	$233.50
Purchase #3	$128.43	8.327%	$139.1244	$139.12	$139.10	$139.10
Purchase #4	$238.88	13.741%	$271.7045	$271.70	$271.70	$271.70
Purchase #5	$61.38	9.705%	$67.3369	$67.34	$67.35	$67.30
Purchase #6	$152.53	13.322%	$172.85	$172.85	$172.85	$172.90
Purchase #7	$63.98	13.508%	$72.6224	$72.62	$72.60	$72.60
7 purchase totals =	$891.45		$993.7075	$993.70	$993.70	$993.60