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	$223.51	6.660%	$238.3958	$238.40	$238.40	$238.40
Purchase #2	$64.52	12.426%	$72.5373	$72.54	$72.55	$72.50
Purchase #3	$18.57	13.816%	$21.1356	$21.14	$21.15	$21.10
Purchase #4	$141.30	7.492%	$151.8862	$151.89	$151.90	$151.90
Purchase #5	$84.54	7.200%	$90.6269	$90.63	$90.65	$90.60
Purchase #6	$104.76	13.561%	$118.9665	$118.97	$118.95	$119.00
Purchase #7	$243.61	4.822%	$255.3569	$255.36	$255.35	$255.40
7 purchase totals =	$880.81		$948.9052	$948.93	$948.95	$948.90