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	$81.59	10.390%	$90.0672	$90.07	$90.05	$90.10
Purchase #2	$11.73	9.140%	$12.8021	$12.80	$12.80	$12.80
Purchase #3	$179.63	9.280%	$196.2997	$196.30	$196.30	$196.30
Purchase #4	$239.38	4.611%	$250.4178	$250.42	$250.40	$250.40
Purchase #5	$238.90	8.201%	$258.4922	$258.49	$258.50	$258.50
Purchase #6	$25.27	13.344%	$28.642	$28.64	$28.65	$28.60
Purchase #7	$86.74	4.361%	$90.5227	$90.52	$90.50	$90.50
7 purchase totals =	$863.24		$927.2437	$927.24	$927.20	$927.20