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	$123.73	13.604%	$140.5622	$140.56	$140.55	$140.60
Purchase #2	$166.41	13.547%	$188.9536	$188.95	$188.95	$189.00
Purchase #3	$146.77	8.773%	$159.6461	$159.65	$159.65	$159.60
Purchase #4	$149.40	12.185%	$167.6044	$167.60	$167.60	$167.60
Purchase #5	$235.67	9.115%	$257.1513	$257.15	$257.15	$257.20
Purchase #6	$208.56	13.793%	$237.3267	$237.33	$237.35	$237.30
Purchase #7	$82.40	9.120%	$89.9149	$89.91	$89.90	$89.90
7 purchase totals =	$1,112.94		$1,241.1592	$1,241.15	$1,241.15	$1,241.20