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	$236.50	4.817%	$247.8922	$247.89	$247.90	$247.90
Purchase #2	$215.91	3.191%	$222.7997	$222.80	$222.80	$222.80
Purchase #3	$174.59	9.734%	$191.5846	$191.58	$191.60	$191.60
Purchase #4	$90.62	6.471%	$96.484	$96.48	$96.50	$96.50
Purchase #5	$250.52	7.491%	$269.2865	$269.29	$269.30	$269.30
Purchase #6	$40.52	11.448%	$45.1587	$45.16	$45.15	$45.20
Purchase #7	$123.37	11.517%	$137.5785	$137.58	$137.60	$137.60
7 purchase totals =	$1,132.03		$1,210.7842	$1,210.78	$1,210.85	$1,210.90