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	$244.66	12.109%	$274.2859	$274.29	$274.30	$274.30
Purchase #2	$203.77	12.846%	$229.9463	$229.95	$229.95	$229.90
Purchase #3	$114.38	7.209%	$122.6257	$122.63	$122.65	$122.60
Purchase #4	$178.78	7.321%	$191.8685	$191.87	$191.85	$191.90
Purchase #5	$161.76	13.201%	$183.1139	$183.11	$183.10	$183.10
Purchase #6	$81.55	4.264%	$85.0273	$85.03	$85.05	$85.00
Purchase #7	$100.90	8.630%	$109.6077	$109.61	$109.60	$109.60
7 purchase totals =	$1,085.80		$1,196.4753	$1,196.49	$1,196.50	$1,196.40