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	$104.73	3.140%	$108.0185	$108.02	$108.00	$108.00
Purchase #2	$70.61	11.572%	$78.781	$78.78	$78.80	$78.80
Purchase #3	$161.34	9.105%	$176.03	$176.03	$176.05	$176.00
Purchase #4	$79.88	12.107%	$89.5511	$89.55	$89.55	$89.60
Purchase #5	$44.28	7.638%	$47.6621	$47.66	$47.65	$47.70
Purchase #6	$43.82	3.241%	$45.2402	$45.24	$45.25	$45.20
Purchase #7	$40.41	9.493%	$44.2461	$44.25	$44.25	$44.20
7 purchase totals =	$545.07		$589.5290	$589.53	$589.55	$589.50