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	$245.79	5.722%	$259.8541	$259.85	$259.85	$259.90
Purchase #2	$112.32	9.443%	$122.9264	$122.93	$122.95	$122.90
Purchase #3	$140.41	8.605%	$152.4923	$152.49	$152.50	$152.50
Purchase #4	$38.41	4.493%	$40.1358	$40.14	$40.15	$40.10
Purchase #5	$136.69	4.586%	$142.9586	$142.96	$142.95	$143.00
Purchase #6	$51.53	6.578%	$54.9196	$54.92	$54.90	$54.90
Purchase #7	$110.36	3.546%	$114.2734	$114.27	$114.25	$114.30
7 purchase totals =	$835.51		$887.5602	$887.56	$887.55	$887.60