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	$44.58	6.348%	$47.4099	$47.41	$47.40	$47.40
Purchase #2	$169.82	4.855%	$178.0648	$178.06	$178.05	$178.10
Purchase #3	$63.29	7.165%	$67.8247	$67.82	$67.80	$67.80
Purchase #4	$146.54	3.463%	$151.6147	$151.61	$151.60	$151.60
Purchase #5	$126.99	8.369%	$137.6178	$137.62	$137.60	$137.60
Purchase #6	$79.27	4.155%	$82.5637	$82.56	$82.55	$82.60
Purchase #7	$174.62	6.344%	$185.6979	$185.70	$185.70	$185.70
7 purchase totals =	$805.11		$850.7935	$850.78	$850.70	$850.80