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	$9.75	5.132%	$10.2504	$10.25	$10.25	$10.30
Purchase #2	$98.47	4.750%	$103.1473	$103.15	$103.15	$103.10
Purchase #3	$150.78	6.257%	$160.2143	$160.21	$160.20	$160.20
Purchase #4	$82.27	12.388%	$92.4616	$92.46	$92.45	$92.50
Purchase #5	$53.43	10.169%	$58.8633	$58.86	$58.85	$58.90
Purchase #6	$138.86	5.526%	$146.5334	$146.53	$146.55	$146.50
Purchase #7	$80.86	12.280%	$90.7896	$90.79	$90.80	$90.80
7 purchase totals =	$614.42		$662.2599	$662.25	$662.25	$662.30