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	$135.67	10.718%	$150.2111	$150.21	$150.20	$150.20
Purchase #2	$225.39	5.411%	$237.5859	$237.59	$237.60	$237.60
Purchase #3	$92.66	12.661%	$104.3917	$104.39	$104.40	$104.40
Purchase #4	$42.46	9.369%	$46.4381	$46.44	$46.45	$46.40
Purchase #5	$196.41	9.602%	$215.2693	$215.27	$215.25	$215.30
Purchase #6	$35.58	7.250%	$38.1596	$38.16	$38.15	$38.20
Purchase #7	$167.65	11.189%	$186.4084	$186.41	$186.40	$186.40
7 purchase totals =	$895.82		$978.4641	$978.47	$978.45	$978.50