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	$64.87	9.595%	$71.0943	$71.09	$71.10	$71.10
Purchase #2	$114.84	7.402%	$123.3405	$123.34	$123.35	$123.30
Purchase #3	$121.35	13.265%	$137.4471	$137.45	$137.45	$137.40
Purchase #4	$83.57	8.559%	$90.7228	$90.72	$90.70	$90.70
Purchase #5	$48.52	13.234%	$54.9411	$54.94	$54.95	$54.90
Purchase #6	$159.49	7.220%	$171.0052	$171.01	$171.00	$171.00
Purchase #7	$247.54	4.867%	$259.5878	$259.59	$259.60	$259.60
7 purchase totals =	$840.18		$908.1388	$908.14	$908.15	$908.00