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	$73.83	8.747%	$80.2879	$80.29	$80.30	$80.30
Purchase #2	$186.98	5.254%	$196.8039	$196.80	$196.80	$196.80
Purchase #3	$223.32	10.559%	$246.9004	$246.90	$246.90	$246.90
Purchase #4	$158.80	5.572%	$167.6483	$167.65	$167.65	$167.60
Purchase #5	$211.66	7.712%	$227.9832	$227.98	$228.00	$228.00
Purchase #6	$151.62	3.216%	$156.4961	$156.50	$156.50	$156.50
Purchase #7	$21.41	12.579%	$24.1032	$24.10	$24.10	$24.10
7 purchase totals =	$1,027.62		$1,100.2230	$1,100.22	$1,100.25	$1,100.20