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	$9.32	13.628%	$10.5901	$10.59	$10.60	$10.60
Purchase #2	$243.72	5.684%	$257.573	$257.57	$257.55	$257.60
Purchase #3	$156.25	12.674%	$176.0531	$176.05	$176.05	$176.10
Purchase #4	$63.30	9.653%	$69.4103	$69.41	$69.40	$69.40
Purchase #5	$85.40	6.536%	$90.9817	$90.98	$91.00	$91.00
Purchase #6	$41.41	3.609%	$42.9045	$42.90	$42.90	$42.90
Purchase #7	$199.70	11.559%	$222.7833	$222.78	$222.80	$222.80
7 purchase totals =	$799.10		$870.2960	$870.28	$870.30	$870.40