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	$80.91	9.183%	$88.34	$88.34	$88.35	$88.30
Purchase #2	$37.51	12.293%	$42.1211	$42.12	$42.10	$42.10
Purchase #3	$113.35	6.577%	$120.805	$120.81	$120.80	$120.80
Purchase #4	$19.32	10.757%	$21.3983	$21.40	$21.40	$21.40
Purchase #5	$113.74	9.283%	$124.2985	$124.30	$124.30	$124.30
Purchase #6	$228.80	11.680%	$255.5238	$255.52	$255.50	$255.50
Purchase #7	$82.92	3.834%	$86.0992	$86.10	$86.10	$86.10
7 purchase totals =	$676.55		$738.5859	$738.59	$738.55	$738.50