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	$222.83	5.629%	$235.3731	$235.37	$235.35	$235.40
Purchase #2	$93.36	5.712%	$98.6927	$98.69	$98.70	$98.70
Purchase #3	$102.86	8.691%	$111.7996	$111.80	$111.80	$111.80
Purchase #4	$148.91	6.778%	$159.0031	$159.00	$159.00	$159.00
Purchase #5	$80.47	13.482%	$91.319	$91.32	$91.30	$91.30
Purchase #6	$168.37	6.624%	$179.5228	$179.52	$179.50	$179.50
Purchase #7	$92.76	12.810%	$104.6426	$104.64	$104.65	$104.60
7 purchase totals =	$909.56		$980.3529	$980.34	$980.30	$980.30