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	$248.76	3.429%	$257.29	$257.29	$257.30	$257.30
Purchase #2	$75.63	4.175%	$78.7876	$78.79	$78.80	$78.80
Purchase #3	$75.69	13.330%	$85.7795	$85.78	$85.80	$85.80
Purchase #4	$63.95	11.733%	$71.4533	$71.45	$71.45	$71.50
Purchase #5	$166.84	5.110%	$175.3655	$175.37	$175.35	$175.40
Purchase #6	$98.34	7.224%	$105.4441	$105.44	$105.45	$105.40
Purchase #7	$127.90	4.229%	$133.3089	$133.31	$133.30	$133.30
7 purchase totals =	$857.11		$907.4289	$907.43	$907.45	$907.50