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	$153.34	13.102%	$173.4306	$173.43	$173.45	$173.40
Purchase #2	$110.92	4.828%	$116.2752	$116.28	$116.30	$116.30
Purchase #3	$249.55	10.602%	$276.0073	$276.01	$276.00	$276.00
Purchase #4	$61.27	9.677%	$67.1991	$67.20	$67.20	$67.20
Purchase #5	$85.47	4.535%	$89.3461	$89.35	$89.35	$89.30
Purchase #6	$72.85	10.219%	$80.2945	$80.29	$80.30	$80.30
Purchase #7	$12.62	6.846%	$13.484	$13.48	$13.50	$13.50
7 purchase totals =	$746.02		$816.0368	$816.04	$816.10	$816.00