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	$248.26	7.555%	$267.016	$267.02	$267.00	$267.00
Purchase #2	$162.34	11.770%	$181.4474	$181.45	$181.45	$181.40
Purchase #3	$54.32	5.437%	$57.2734	$57.27	$57.25	$57.30
Purchase #4	$132.96	3.773%	$137.9766	$137.98	$138.00	$138.00
Purchase #5	$42.72	6.327%	$45.4229	$45.42	$45.40	$45.40
Purchase #6	$69.27	13.215%	$78.424	$78.42	$78.40	$78.40
Purchase #7	$75.28	11.468%	$83.9131	$83.91	$83.90	$83.90
7 purchase totals =	$785.15		$851.4734	$851.47	$851.40	$851.40