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	$66.72	4.560%	$69.7624	$69.76	$69.75	$69.80
Purchase #2	$139.46	11.247%	$155.1451	$155.15	$155.15	$155.10
Purchase #3	$63.45	6.352%	$67.4803	$67.48	$67.50	$67.50
Purchase #4	$78.82	8.506%	$85.5244	$85.52	$85.50	$85.50
Purchase #5	$239.66	6.617%	$255.5183	$255.52	$255.50	$255.50
Purchase #6	$162.51	9.616%	$178.137	$178.14	$178.15	$178.10
Purchase #7	$68.71	13.566%	$78.0312	$78.03	$78.05	$78.00
7 purchase totals =	$819.33		$889.5987	$889.60	$889.60	$889.50