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	$91.98	8.502%	$99.8001	$99.80	$99.80	$99.80
Purchase #2	$86.87	13.753%	$98.8172	$98.82	$98.80	$98.80
Purchase #3	$16.47	10.643%	$18.2229	$18.22	$18.20	$18.20
Purchase #4	$148.67	13.602%	$168.8921	$168.89	$168.90	$168.90
Purchase #5	$55.98	9.763%	$61.4453	$61.45	$61.45	$61.40
Purchase #6	$11.42	5.777%	$12.0797	$12.08	$12.10	$12.10
Purchase #7	$126.42	7.772%	$136.2454	$136.25	$136.25	$136.20
7 purchase totals =	$537.81		$595.5027	$595.51	$595.50	$595.40