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	$70.87	12.244%	$79.5473	$79.55	$79.55	$79.50
Purchase #2	$229.51	12.380%	$257.9233	$257.92	$257.90	$257.90
Purchase #3	$76.47	8.697%	$83.1206	$83.12	$83.10	$83.10
Purchase #4	$167.51	4.786%	$175.527	$175.53	$175.55	$175.50
Purchase #5	$95.83	12.220%	$107.5404	$107.54	$107.55	$107.50
Purchase #6	$187.96	4.778%	$196.9407	$196.94	$196.95	$196.90
Purchase #7	$60.97	10.664%	$67.4718	$67.47	$67.45	$67.50
7 purchase totals =	$889.12		$968.0711	$968.07	$968.05	$967.90