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	$246.29	9.601%	$269.9363	$269.94	$269.95	$269.90
Purchase #2	$208.34	5.146%	$219.0612	$219.06	$219.05	$219.10
Purchase #3	$138.82	9.747%	$152.3508	$152.35	$152.35	$152.40
Purchase #4	$132.89	5.302%	$139.9358	$139.94	$139.95	$139.90
Purchase #5	$234.65	4.790%	$245.8897	$245.89	$245.90	$245.90
Purchase #6	$120.34	5.849%	$127.3787	$127.38	$127.40	$127.40
Purchase #7	$114.82	9.709%	$125.9679	$125.97	$125.95	$126.00
7 purchase totals =	$1,196.15		$1,280.5204	$1,280.53	$1,280.55	$1,280.60