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	$100.83	10.178%	$111.0925	$111.09	$111.10	$111.10
Purchase #2	$209.54	11.397%	$233.4213	$233.42	$233.40	$233.40
Purchase #3	$62.94	3.622%	$65.2197	$65.22	$65.20	$65.20
Purchase #4	$221.90	4.267%	$231.3685	$231.37	$231.35	$231.40
Purchase #5	$202.43	10.491%	$223.6669	$223.67	$223.65	$223.70
Purchase #6	$168.64	10.310%	$186.0268	$186.03	$186.05	$186.00
Purchase #7	$171.77	10.222%	$189.3283	$189.33	$189.35	$189.30
7 purchase totals =	$1,138.05		$1,240.1240	$1,240.13	$1,240.10	$1,240.10