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	$84.69	6.793%	$90.443	$90.44	$90.45	$90.40
Purchase #2	$162.64	9.461%	$178.0274	$178.03	$178.05	$178.00
Purchase #3	$48.66	4.116%	$50.6628	$50.66	$50.65	$50.70
Purchase #4	$68.88	5.494%	$72.6643	$72.66	$72.65	$72.70
Purchase #5	$82.48	9.200%	$90.0682	$90.07	$90.05	$90.10
Purchase #6	$179.63	4.425%	$187.5786	$187.58	$187.60	$187.60
Purchase #7	$217.93	12.679%	$245.5613	$245.56	$245.55	$245.60
7 purchase totals =	$844.91		$915.0056	$915.00	$915.00	$915.10