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	$78.84	13.759%	$89.6876	$89.69	$89.70	$89.70
Purchase #2	$196.63	13.178%	$222.5419	$222.54	$222.55	$222.50
Purchase #3	$19.82	4.116%	$20.6358	$20.64	$20.65	$20.60
Purchase #4	$113.63	5.112%	$119.4388	$119.44	$119.45	$119.40
Purchase #5	$185.40	6.300%	$197.0802	$197.08	$197.10	$197.10
Purchase #6	$66.86	5.235%	$70.3601	$70.36	$70.35	$70.40
Purchase #7	$54.95	10.427%	$60.6796	$60.68	$60.70	$60.70
7 purchase totals =	$716.13		$780.4240	$780.43	$780.50	$780.40