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	$36.66	5.527%	$38.6862	$38.69	$38.70	$38.70
Purchase #2	$155.85	10.252%	$171.8277	$171.83	$171.85	$171.80
Purchase #3	$139.68	7.867%	$150.6686	$150.67	$150.65	$150.70
Purchase #4	$56.74	4.330%	$59.1968	$59.20	$59.20	$59.20
Purchase #5	$10.79	6.447%	$11.4856	$11.49	$11.50	$11.50
Purchase #6	$116.49	9.132%	$127.1279	$127.13	$127.15	$127.10
Purchase #7	$178.26	4.471%	$186.23	$186.23	$186.25	$186.20
7 purchase totals =	$694.47		$745.2228	$745.24	$745.30	$745.20