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	$10.50	10.524%	$11.605	$11.61	$11.60	$11.60
Purchase #2	$186.27	4.383%	$194.4342	$194.43	$194.45	$194.40
Purchase #3	$170.74	6.302%	$181.5	$181.50	$181.50	$181.50
Purchase #4	$152.42	11.256%	$169.5764	$169.58	$169.60	$169.60
Purchase #5	$59.54	10.386%	$65.7238	$65.72	$65.70	$65.70
Purchase #6	$146.27	6.314%	$155.5055	$155.51	$155.50	$155.50
Purchase #7	$35.73	6.728%	$38.1339	$38.13	$38.15	$38.10
7 purchase totals =	$761.47		$816.4788	$816.48	$816.50	$816.40