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	$92.30	12.834%	$104.1458	$104.15	$104.15	$104.10
Purchase #2	$239.36	10.208%	$263.7939	$263.79	$263.80	$263.80
Purchase #3	$101.90	9.325%	$111.4022	$111.40	$111.40	$111.40
Purchase #4	$119.95	9.843%	$131.7567	$131.76	$131.75	$131.80
Purchase #5	$13.51	10.855%	$14.9765	$14.98	$15.00	$15.00
Purchase #6	$130.69	4.233%	$136.2221	$136.22	$136.20	$136.20
Purchase #7	$159.90	9.146%	$174.5245	$174.52	$174.50	$174.50
7 purchase totals =	$857.61		$936.8217	$936.82	$936.80	$936.80