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	$17.31	9.805%	$19.0072	$19.01	$19.00	$19.00
Purchase #2	$89.44	12.553%	$100.6674	$100.67	$100.65	$100.70
Purchase #3	$60.67	11.559%	$67.6828	$67.68	$67.70	$67.70
Purchase #4	$210.75	6.667%	$224.8007	$224.80	$224.80	$224.80
Purchase #5	$35.51	6.702%	$37.8899	$37.89	$37.90	$37.90
Purchase #6	$55.75	10.320%	$61.5034	$61.50	$61.50	$61.50
Purchase #7	$166.60	9.105%	$181.7689	$181.77	$181.75	$181.80
7 purchase totals =	$636.03		$693.3203	$693.32	$693.30	$693.40