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	$73.47	8.214%	$79.5048	$79.50	$79.50	$79.50
Purchase #2	$165.78	10.311%	$182.8736	$182.87	$182.85	$182.90
Purchase #3	$225.49	11.686%	$251.8408	$251.84	$251.85	$251.80
Purchase #4	$228.81	11.697%	$255.5739	$255.57	$255.55	$255.60
Purchase #5	$93.64	6.855%	$100.059	$100.06	$100.05	$100.10
Purchase #6	$137.78	5.107%	$144.8164	$144.82	$144.80	$144.80
Purchase #7	$233.76	4.619%	$244.5574	$244.56	$244.55	$244.60
7 purchase totals =	$1,158.73		$1,259.2259	$1,259.22	$1,259.15	$1,259.30