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	$36.48	5.690%	$38.5557	$38.56	$38.55	$38.60
Purchase #2	$108.39	11.560%	$120.9199	$120.92	$120.90	$120.90
Purchase #3	$248.69	13.382%	$281.9697	$281.97	$281.95	$282.00
Purchase #4	$30.49	12.584%	$34.3269	$34.33	$34.35	$34.30
Purchase #5	$172.25	7.711%	$185.5322	$185.53	$185.55	$185.50
Purchase #6	$117.27	8.569%	$127.3189	$127.32	$127.30	$127.30
Purchase #7	$179.41	4.426%	$187.3507	$187.35	$187.35	$187.40
7 purchase totals =	$892.98		$975.9740	$975.98	$975.95	$976.00