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	$139.57	13.304%	$158.1384	$158.14	$158.15	$158.10
Purchase #2	$191.52	8.776%	$208.3278	$208.33	$208.35	$208.30
Purchase #3	$82.97	9.400%	$90.7692	$90.77	$90.75	$90.80
Purchase #4	$215.51	5.420%	$227.1906	$227.19	$227.20	$227.20
Purchase #5	$46.43	9.407%	$50.7977	$50.80	$50.80	$50.80
Purchase #6	$192.51	8.595%	$209.0562	$209.06	$209.05	$209.10
Purchase #7	$177.34	3.434%	$183.4299	$183.43	$183.45	$183.40
7 purchase totals =	$1,045.85		$1,127.7098	$1,127.72	$1,127.75	$1,127.70