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	$225.48	5.539%	$237.9693	$237.97	$237.95	$238.00
Purchase #2	$158.70	5.739%	$167.8078	$167.81	$167.80	$167.80
Purchase #3	$37.29	8.729%	$40.545	$40.55	$40.55	$40.50
Purchase #4	$96.63	7.731%	$104.1005	$104.10	$104.10	$104.10
Purchase #5	$127.93	10.456%	$141.3064	$141.31	$141.30	$141.30
Purchase #6	$86.65	3.641%	$89.8049	$89.80	$89.80	$89.80
Purchase #7	$47.95	12.739%	$54.0584	$54.06	$54.05	$54.10
7 purchase totals =	$780.63		$835.5923	$835.60	$835.55	$835.60