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	$18.34	5.640%	$19.3744	$19.37	$19.35	$19.40
Purchase #2	$223.82	9.419%	$244.9016	$244.90	$244.90	$244.90
Purchase #3	$166.62	4.712%	$174.4711	$174.47	$174.45	$174.50
Purchase #4	$121.29	8.670%	$131.8058	$131.81	$131.80	$131.80
Purchase #5	$123.99	13.475%	$140.6977	$140.70	$140.70	$140.70
Purchase #6	$86.60	4.167%	$90.2086	$90.21	$90.20	$90.20
Purchase #7	$232.55	10.276%	$256.4468	$256.45	$256.45	$256.40
7 purchase totals =	$973.21		$1,057.9060	$1,057.91	$1,057.85	$1,057.90