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	$230.91	12.300%	$259.3119	$259.31	$259.30	$259.30
Purchase #2	$117.89	12.744%	$132.9139	$132.91	$132.90	$132.90
Purchase #3	$200.63	12.183%	$225.0728	$225.07	$225.05	$225.10
Purchase #4	$222.55	11.826%	$248.8688	$248.87	$248.85	$248.90
Purchase #5	$126.44	12.715%	$142.5168	$142.52	$142.50	$142.50
Purchase #6	$233.61	12.621%	$263.0939	$263.09	$263.10	$263.10
Purchase #7	$209.53	9.446%	$229.3222	$229.32	$229.30	$229.30
7 purchase totals =	$1,341.56		$1,501.1003	$1,501.09	$1,501.00	$1,501.10