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	$64.48	12.594%	$72.6006	$72.60	$72.60	$72.60
Purchase #2	$208.27	8.172%	$225.2898	$225.29	$225.30	$225.30
Purchase #3	$18.88	12.566%	$21.2525	$21.25	$21.25	$21.30
Purchase #4	$90.52	13.293%	$102.5528	$102.55	$102.55	$102.60
Purchase #5	$115.91	13.608%	$131.683	$131.68	$131.70	$131.70
Purchase #6	$79.56	8.275%	$86.1436	$86.14	$86.15	$86.10
Purchase #7	$200.40	5.122%	$210.6645	$210.66	$210.65	$210.70
7 purchase totals =	$778.02		$850.1868	$850.17	$850.20	$850.30