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	$226.77	13.120%	$256.5222	$256.52	$256.50	$256.50
Purchase #2	$190.48	12.260%	$213.8328	$213.83	$213.85	$213.80
Purchase #3	$86.28	3.626%	$89.4085	$89.41	$89.40	$89.40
Purchase #4	$190.49	5.168%	$200.3345	$200.33	$200.35	$200.30
Purchase #5	$128.81	7.618%	$138.6227	$138.62	$138.60	$138.60
Purchase #6	$24.88	4.371%	$25.9675	$25.97	$25.95	$26.00
Purchase #7	$61.88	9.304%	$67.6373	$67.64	$67.65	$67.60
7 purchase totals =	$909.59		$992.3255	$992.32	$992.30	$992.20