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	$22.59	12.295%	$25.3674	$25.37	$25.35	$25.40
Purchase #2	$89.86	6.271%	$95.4951	$95.50	$95.50	$95.50
Purchase #3	$22.27	8.319%	$24.1226	$24.12	$24.10	$24.10
Purchase #4	$105.56	3.682%	$109.4467	$109.45	$109.45	$109.40
Purchase #5	$162.43	3.161%	$167.5644	$167.56	$167.55	$167.60
Purchase #6	$115.91	11.835%	$129.6279	$129.63	$129.65	$129.60
Purchase #7	$63.26	13.847%	$72.0196	$72.02	$72.00	$72.00
7 purchase totals =	$581.88		$623.6437	$623.65	$623.60	$623.60