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	$44.53	12.789%	$50.2249	$50.22	$50.20	$50.20
Purchase #2	$12.68	5.544%	$13.383	$13.38	$13.40	$13.40
Purchase #3	$103.59	7.372%	$111.2267	$111.23	$111.25	$111.20
Purchase #4	$55.34	7.842%	$59.6798	$59.68	$59.70	$59.70
Purchase #5	$35.36	10.523%	$39.0809	$39.08	$39.10	$39.10
Purchase #6	$63.76	13.702%	$72.4964	$72.50	$72.50	$72.50
Purchase #7	$194.27	4.737%	$203.4726	$203.47	$203.45	$203.50
7 purchase totals =	$509.53		$549.5643	$549.56	$549.60	$549.60