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	$106.69	13.801%	$121.4143	$121.41	$121.40	$121.40
Purchase #2	$189.29	3.396%	$195.7183	$195.72	$195.70	$195.70
Purchase #3	$73.70	6.771%	$78.6902	$78.69	$78.70	$78.70
Purchase #4	$126.52	12.242%	$142.0086	$142.01	$142.00	$142.00
Purchase #5	$82.37	11.615%	$91.9373	$91.94	$91.95	$91.90
Purchase #6	$181.50	10.634%	$200.8007	$200.80	$200.80	$200.80
Purchase #7	$140.83	5.132%	$148.0574	$148.06	$148.05	$148.10
7 purchase totals =	$900.90		$978.6268	$978.63	$978.60	$978.60