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	$156.63	6.114%	$166.2064	$166.21	$166.20	$166.20
Purchase #2	$116.45	9.826%	$127.8924	$127.89	$127.90	$127.90
Purchase #3	$121.94	12.250%	$136.8777	$136.88	$136.90	$136.90
Purchase #4	$86.48	3.407%	$89.4264	$89.43	$89.45	$89.40
Purchase #5	$111.33	9.683%	$122.1101	$122.11	$122.10	$122.10
Purchase #6	$148.54	9.401%	$162.5042	$162.50	$162.50	$162.50
Purchase #7	$189.65	11.691%	$211.822	$211.82	$211.80	$211.80
7 purchase totals =	$931.02		$1,016.8392	$1,016.84	$1,016.85	$1,016.80