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	$75.80	12.739%	$85.4562	$85.46	$85.45	$85.50
Purchase #2	$92.40	12.825%	$104.2503	$104.25	$104.25	$104.30
Purchase #3	$199.81	9.750%	$219.2915	$219.29	$219.30	$219.30
Purchase #4	$167.58	13.537%	$190.2653	$190.27	$190.25	$190.30
Purchase #5	$161.37	5.254%	$169.8484	$169.85	$169.85	$169.80
Purchase #6	$18.42	9.338%	$20.1401	$20.14	$20.15	$20.10
Purchase #7	$208.70	8.559%	$226.5626	$226.56	$226.55	$226.60
7 purchase totals =	$924.08		$1,015.8144	$1,015.82	$1,015.80	$1,015.90