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	$63.78	12.560%	$71.7908	$71.79	$71.80	$71.80
Purchase #2	$83.45	9.591%	$91.4537	$91.45	$91.45	$91.50
Purchase #3	$83.69	12.405%	$94.0717	$94.07	$94.05	$94.10
Purchase #4	$201.56	8.714%	$219.1239	$219.12	$219.10	$219.10
Purchase #5	$177.54	7.390%	$190.6602	$190.66	$190.65	$190.70
Purchase #6	$65.48	10.540%	$72.3816	$72.38	$72.40	$72.40
Purchase #7	$75.47	4.641%	$78.9726	$78.97	$78.95	$79.00
7 purchase totals =	$750.97		$818.4545	$818.44	$818.40	$818.60