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	$40.86	7.395%	$43.8816	$43.88	$43.90	$43.90
Purchase #2	$224.77	7.457%	$241.5311	$241.53	$241.55	$241.50
Purchase #3	$110.46	11.634%	$123.3109	$123.31	$123.30	$123.30
Purchase #4	$190.55	9.383%	$208.4293	$208.43	$208.45	$208.40
Purchase #5	$87.26	6.479%	$92.9136	$92.91	$92.90	$92.90
Purchase #6	$69.44	12.846%	$78.3603	$78.36	$78.35	$78.40
Purchase #7	$114.48	11.167%	$127.264	$127.26	$127.25	$127.30
7 purchase totals =	$837.82		$915.6908	$915.68	$915.70	$915.70