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	$8.62	10.108%	$9.4913	$9.49	$9.50	$9.50
Purchase #2	$61.88	6.278%	$65.7648	$65.76	$65.75	$65.80
Purchase #3	$223.55	3.225%	$230.7595	$230.76	$230.75	$230.80
Purchase #4	$240.45	6.171%	$255.2882	$255.29	$255.30	$255.30
Purchase #5	$161.70	3.629%	$167.5681	$167.57	$167.55	$167.60
Purchase #6	$179.61	9.390%	$196.4754	$196.48	$196.50	$196.50
Purchase #7	$235.80	5.253%	$248.1866	$248.19	$248.20	$248.20
7 purchase totals =	$1,111.61		$1,173.5339	$1,173.54	$1,173.55	$1,173.70