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	$40.87	6.720%	$43.6165	$43.62	$43.60	$43.60
Purchase #2	$33.69	12.788%	$37.9983	$38.00	$38.00	$38.00
Purchase #3	$65.71	9.278%	$71.8066	$71.81	$71.80	$71.80
Purchase #4	$56.55	4.690%	$59.2022	$59.20	$59.20	$59.20
Purchase #5	$112.72	7.293%	$120.9407	$120.94	$120.95	$120.90
Purchase #6	$61.82	9.233%	$67.5278	$67.53	$67.55	$67.50
Purchase #7	$244.83	9.353%	$267.7289	$267.73	$267.75	$267.70
7 purchase totals =	$616.19		$668.8210	$668.83	$668.85	$668.70