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	$74.95	11.278%	$83.4029	$83.40	$83.40	$83.40
Purchase #2	$100.74	10.665%	$111.4839	$111.48	$111.50	$111.50
Purchase #3	$246.50	7.436%	$264.8297	$264.83	$264.85	$264.80
Purchase #4	$193.84	9.848%	$212.9294	$212.93	$212.95	$212.90
Purchase #5	$71.99	6.608%	$76.7471	$76.75	$76.75	$76.70
Purchase #6	$91.63	8.398%	$99.3251	$99.33	$99.35	$99.30
Purchase #7	$25.59	12.564%	$28.8051	$28.81	$28.80	$28.80
7 purchase totals =	$805.24		$877.5232	$877.53	$877.60	$877.40