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	$244.65	3.704%	$253.7118	$253.71	$253.70	$253.70
Purchase #2	$165.71	6.607%	$176.6585	$176.66	$176.65	$176.70
Purchase #3	$235.87	9.210%	$257.5936	$257.59	$257.60	$257.60
Purchase #4	$101.29	11.456%	$112.8938	$112.89	$112.90	$112.90
Purchase #5	$41.76	4.662%	$43.7069	$43.71	$43.70	$43.70
Purchase #6	$105.25	13.219%	$119.163	$119.16	$119.15	$119.20
Purchase #7	$33.47	6.341%	$35.5923	$35.59	$35.60	$35.60
7 purchase totals =	$928.00		$999.3199	$999.31	$999.30	$999.40