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	$137.58	3.651%	$142.603	$142.60	$142.60	$142.60
Purchase #2	$33.98	13.143%	$38.446	$38.45	$38.45	$38.40
Purchase #3	$238.40	11.125%	$264.922	$264.92	$264.90	$264.90
Purchase #4	$73.64	9.800%	$80.8567	$80.86	$80.85	$80.90
Purchase #5	$81.58	10.527%	$90.1679	$90.17	$90.15	$90.20
Purchase #6	$65.91	12.131%	$73.9055	$73.91	$73.90	$73.90
Purchase #7	$84.86	4.748%	$88.8892	$88.89	$88.90	$88.90
7 purchase totals =	$715.95		$779.7903	$779.80	$779.75	$779.80