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	$34.43	12.554%	$38.7523	$38.75	$38.75	$38.80
Purchase #2	$113.65	12.368%	$127.7062	$127.71	$127.70	$127.70
Purchase #3	$81.89	13.408%	$92.8698	$92.87	$92.85	$92.90
Purchase #4	$109.58	3.619%	$113.5457	$113.55	$113.55	$113.50
Purchase #5	$176.75	4.738%	$185.1244	$185.12	$185.10	$185.10
Purchase #6	$233.70	6.745%	$249.4631	$249.46	$249.45	$249.50
Purchase #7	$181.68	4.497%	$189.8501	$189.85	$189.85	$189.90
7 purchase totals =	$931.68		$997.3116	$997.31	$997.25	$997.40