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	$88.55	10.543%	$97.8858	$97.89	$97.90	$97.90
Purchase #2	$48.81	7.299%	$52.3726	$52.37	$52.35	$52.40
Purchase #3	$41.66	5.643%	$44.0109	$44.01	$44.00	$44.00
Purchase #4	$95.36	10.137%	$105.0266	$105.03	$105.05	$105.00
Purchase #5	$92.70	8.809%	$100.8659	$100.87	$100.85	$100.90
Purchase #6	$37.47	7.651%	$40.3368	$40.34	$40.35	$40.30
Purchase #7	$141.77	7.209%	$151.9902	$151.99	$152.00	$152.00
7 purchase totals =	$546.32		$592.4888	$592.50	$592.50	$592.50