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	$108.78	10.849%	$120.5815	$120.58	$120.60	$120.60
Purchase #2	$241.48	3.553%	$250.0598	$250.06	$250.05	$250.10
Purchase #3	$39.35	11.744%	$43.9713	$43.97	$43.95	$44.00
Purchase #4	$211.62	8.599%	$229.8172	$229.82	$229.80	$229.80
Purchase #5	$73.64	5.830%	$77.9332	$77.93	$77.95	$77.90
Purchase #6	$143.43	3.574%	$148.5562	$148.56	$148.55	$148.60
Purchase #7	$108.53	13.417%	$123.0915	$123.09	$123.10	$123.10
7 purchase totals =	$926.83		$994.0107	$994.01	$994.00	$994.10