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	$129.79	6.131%	$137.7474	$137.75	$137.75	$137.70
Purchase #2	$29.95	11.300%	$33.3344	$33.33	$33.35	$33.30
Purchase #3	$90.48	6.705%	$96.5467	$96.55	$96.55	$96.50
Purchase #4	$52.86	4.735%	$55.3629	$55.36	$55.35	$55.40
Purchase #5	$24.28	13.327%	$27.5158	$27.52	$27.50	$27.50
Purchase #6	$104.70	11.593%	$116.8379	$116.84	$116.85	$116.80
Purchase #7	$108.30	3.362%	$111.941	$111.94	$111.95	$111.90
7 purchase totals =	$540.36		$579.2861	$579.29	$579.30	$579.10