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	$73.90	5.788%	$78.1773	$78.18	$78.20	$78.20
Purchase #2	$233.51	11.149%	$259.544	$259.54	$259.55	$259.50
Purchase #3	$115.75	8.709%	$125.8307	$125.83	$125.85	$125.80
Purchase #4	$18.84	11.466%	$21.0002	$21.00	$21.00	$21.00
Purchase #5	$132.78	10.192%	$146.3129	$146.31	$146.30	$146.30
Purchase #6	$229.41	11.546%	$255.8977	$255.90	$255.90	$255.90
Purchase #7	$131.76	6.868%	$140.8093	$140.81	$140.80	$140.80
7 purchase totals =	$935.95		$1,027.5721	$1,027.57	$1,027.60	$1,027.50