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	$158.63	7.140%	$169.9562	$169.96	$169.95	$170.00
Purchase #2	$33.93	9.387%	$37.115	$37.12	$37.10	$37.10
Purchase #3	$29.54	5.431%	$31.1443	$31.14	$31.15	$31.10
Purchase #4	$81.85	9.204%	$89.3835	$89.38	$89.40	$89.40
Purchase #5	$124.69	5.450%	$131.4856	$131.49	$131.50	$131.50
Purchase #6	$61.97	7.278%	$66.4802	$66.48	$66.50	$66.50
Purchase #7	$119.95	3.141%	$123.7176	$123.72	$123.70	$123.70
7 purchase totals =	$610.56		$649.2824	$649.29	$649.30	$649.30