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	$59.49	12.862%	$67.1416	$67.14	$67.15	$67.10
Purchase #2	$22.79	6.668%	$24.3096	$24.31	$24.30	$24.30
Purchase #3	$199.48	8.122%	$215.6818	$215.68	$215.70	$215.70
Purchase #4	$214.39	3.139%	$221.1197	$221.12	$221.10	$221.10
Purchase #5	$122.85	13.584%	$139.5379	$139.54	$139.55	$139.50
Purchase #6	$138.86	3.108%	$143.1758	$143.18	$143.20	$143.20
Purchase #7	$71.60	9.460%	$78.3734	$78.37	$78.35	$78.40
7 purchase totals =	$829.46		$889.3398	$889.34	$889.35	$889.30