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	$244.63	4.578%	$255.8292	$255.83	$255.85	$255.80
Purchase #2	$188.33	10.455%	$208.0199	$208.02	$208.00	$208.00
Purchase #3	$6.77	8.250%	$7.3285	$7.33	$7.35	$7.30
Purchase #4	$219.45	8.509%	$238.123	$238.12	$238.10	$238.10
Purchase #5	$59.51	5.739%	$62.9253	$62.93	$62.95	$62.90
Purchase #6	$101.60	11.756%	$113.5441	$113.54	$113.55	$113.50
Purchase #7	$96.70	12.562%	$108.8475	$108.85	$108.85	$108.80
7 purchase totals =	$916.99		$994.6175	$994.62	$994.65	$994.40