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	$94.94	7.357%	$101.9247	$101.92	$101.90	$101.90
Purchase #2	$142.61	4.144%	$148.5198	$148.52	$148.50	$148.50
Purchase #3	$74.66	5.499%	$78.7656	$78.77	$78.75	$78.80
Purchase #4	$21.82	5.668%	$23.0568	$23.06	$23.05	$23.10
Purchase #5	$36.52	11.116%	$40.5796	$40.58	$40.60	$40.60
Purchase #6	$103.86	4.213%	$108.2356	$108.24	$108.25	$108.20
Purchase #7	$50.70	7.821%	$54.6652	$54.67	$54.65	$54.70
7 purchase totals =	$525.11		$555.7473	$555.76	$555.70	$555.80