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	$73.80	8.256%	$79.8929	$79.89	$79.90	$79.90
Purchase #2	$110.34	8.763%	$120.0091	$120.01	$120.00	$120.00
Purchase #3	$186.34	11.789%	$208.3076	$208.31	$208.30	$208.30
Purchase #4	$229.51	6.530%	$244.497	$244.50	$244.50	$244.50
Purchase #5	$142.79	8.153%	$154.4317	$154.43	$154.45	$154.40
Purchase #6	$96.52	4.488%	$100.8518	$100.85	$100.85	$100.90
Purchase #7	$28.55	11.523%	$31.8398	$31.84	$31.85	$31.80
7 purchase totals =	$867.85		$939.8299	$939.83	$939.85	$939.80