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	$11.71	9.313%	$12.8006	$12.80	$12.80	$12.80
Purchase #2	$83.90	6.241%	$89.1362	$89.14	$89.15	$89.10
Purchase #3	$52.74	3.664%	$54.6724	$54.67	$54.65	$54.70
Purchase #4	$95.60	10.759%	$105.8856	$105.89	$105.90	$105.90
Purchase #5	$129.70	11.596%	$144.74	$144.74	$144.75	$144.70
Purchase #6	$110.69	8.124%	$119.6825	$119.68	$119.70	$119.70
Purchase #7	$227.38	11.721%	$254.0312	$254.03	$254.05	$254.00
7 purchase totals =	$711.72		$780.9485	$780.95	$781.00	$780.90