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	$39.29	5.718%	$41.5366	$41.54	$41.55	$41.50
Purchase #2	$184.29	10.192%	$203.0728	$203.07	$203.05	$203.10
Purchase #3	$120.66	9.142%	$131.6907	$131.69	$131.70	$131.70
Purchase #4	$53.60	13.828%	$61.0118	$61.01	$61.00	$61.00
Purchase #5	$235.79	5.483%	$248.7184	$248.72	$248.70	$248.70
Purchase #6	$172.64	10.426%	$190.6394	$190.64	$190.65	$190.60
Purchase #7	$117.42	12.269%	$131.8263	$131.83	$131.85	$131.80
7 purchase totals =	$923.69		$1,008.4960	$1,008.50	$1,008.50	$1,008.40