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	$114.43	11.290%	$127.3491	$127.35	$127.35	$127.30
Purchase #2	$240.56	12.372%	$270.3221	$270.32	$270.30	$270.30
Purchase #3	$61.80	12.132%	$69.2976	$69.30	$69.30	$69.30
Purchase #4	$54.29	7.503%	$58.3634	$58.36	$58.35	$58.40
Purchase #5	$42.43	6.583%	$45.2232	$45.22	$45.20	$45.20
Purchase #6	$195.37	9.693%	$214.3072	$214.31	$214.30	$214.30
Purchase #7	$52.58	12.411%	$59.1057	$59.11	$59.10	$59.10
7 purchase totals =	$761.46		$843.9683	$843.97	$843.90	$843.90