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	$100.28	8.742%	$109.0465	$109.05	$109.05	$109.00
Purchase #2	$76.65	8.778%	$83.3783	$83.38	$83.40	$83.40
Purchase #3	$223.52	11.168%	$248.4827	$248.48	$248.50	$248.50
Purchase #4	$193.41	6.287%	$205.5697	$205.57	$205.55	$205.60
Purchase #5	$90.95	10.235%	$100.2587	$100.26	$100.25	$100.30
Purchase #6	$130.26	9.611%	$142.7793	$142.78	$142.80	$142.80
Purchase #7	$42.37	4.196%	$44.1478	$44.15	$44.15	$44.10
7 purchase totals =	$857.44		$933.6630	$933.67	$933.70	$933.70