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	$229.44	11.539%	$255.9151	$255.92	$255.90	$255.90
Purchase #2	$248.93	13.215%	$281.8261	$281.83	$281.85	$281.80
Purchase #3	$89.75	10.142%	$98.8524	$98.85	$98.85	$98.90
Purchase #4	$17.86	6.553%	$19.0304	$19.03	$19.05	$19.00
Purchase #5	$45.44	11.538%	$50.6829	$50.68	$50.70	$50.70
Purchase #6	$128.37	6.853%	$137.1672	$137.17	$137.15	$137.20
Purchase #7	$104.53	4.767%	$109.5129	$109.51	$109.50	$109.50
7 purchase totals =	$864.32		$952.9870	$952.99	$953.00	$953.00