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	$66.46	8.353%	$72.0114	$72.01	$72.00	$72.00
Purchase #2	$38.97	6.326%	$41.4352	$41.44	$41.45	$41.40
Purchase #3	$45.82	5.506%	$48.3428	$48.34	$48.35	$48.30
Purchase #4	$146.93	12.270%	$164.9583	$164.96	$164.95	$165.00
Purchase #5	$85.71	10.547%	$94.7498	$94.75	$94.75	$94.70
Purchase #6	$75.43	6.186%	$80.0961	$80.10	$80.10	$80.10
Purchase #7	$61.38	10.503%	$67.8267	$67.83	$67.85	$67.80
7 purchase totals =	$520.70		$569.4203	$569.43	$569.45	$569.30