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	$200.71	7.149%	$215.0588	$215.06	$215.05	$215.10
Purchase #2	$164.90	8.463%	$178.8555	$178.86	$178.85	$178.90
Purchase #3	$24.56	13.814%	$27.9527	$27.95	$27.95	$28.00
Purchase #4	$89.77	5.563%	$94.7639	$94.76	$94.75	$94.80
Purchase #5	$9.78	11.326%	$10.8877	$10.89	$10.90	$10.90
Purchase #6	$24.83	11.528%	$27.6924	$27.69	$27.70	$27.70
Purchase #7	$58.86	11.831%	$65.8237	$65.82	$65.80	$65.80
7 purchase totals =	$573.41		$621.0347	$621.03	$621.00	$621.20