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	$85.81	4.838%	$89.9615	$89.96	$89.95	$90.00
Purchase #2	$36.99	5.377%	$38.979	$38.98	$39.00	$39.00
Purchase #3	$220.79	8.198%	$238.8904	$238.89	$238.90	$238.90
Purchase #4	$57.52	5.256%	$60.5433	$60.54	$60.55	$60.50
Purchase #5	$195.68	11.238%	$217.6705	$217.67	$217.65	$217.70
Purchase #6	$143.45	5.709%	$151.6396	$151.64	$151.65	$151.60
Purchase #7	$43.72	4.840%	$45.836	$45.84	$45.85	$45.80
7 purchase totals =	$783.96		$843.5203	$843.52	$843.55	$843.50