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	$41.68	5.641%	$44.0312	$44.03	$44.05	$44.00
Purchase #2	$239.96	12.461%	$269.8614	$269.86	$269.85	$269.90
Purchase #3	$168.95	6.655%	$180.1936	$180.19	$180.20	$180.20
Purchase #4	$84.87	6.596%	$90.468	$90.47	$90.45	$90.50
Purchase #5	$70.77	11.187%	$78.687	$78.69	$78.70	$78.70
Purchase #6	$158.58	8.803%	$172.5398	$172.54	$172.55	$172.50
Purchase #7	$133.65	8.374%	$144.8419	$144.84	$144.85	$144.80
7 purchase totals =	$898.46		$980.6229	$980.62	$980.65	$980.60