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	$72.66	10.365%	$80.1912	$80.19	$80.20	$80.20
Purchase #2	$127.98	11.671%	$142.9165	$142.92	$142.90	$142.90
Purchase #3	$156.46	9.588%	$171.4614	$171.46	$171.45	$171.50
Purchase #4	$45.48	10.624%	$50.3118	$50.31	$50.30	$50.30
Purchase #5	$121.34	6.337%	$129.0293	$129.03	$129.05	$129.00
Purchase #6	$234.65	10.722%	$259.8092	$259.81	$259.80	$259.80
Purchase #7	$136.95	5.842%	$144.9506	$144.95	$144.95	$145.00
7 purchase totals =	$895.52		$978.6700	$978.67	$978.65	$978.70