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	$208.31	10.541%	$230.268	$230.27	$230.25	$230.30
Purchase #2	$216.66	4.800%	$227.0597	$227.06	$227.05	$227.10
Purchase #3	$31.61	11.705%	$35.31	$35.31	$35.30	$35.30
Purchase #4	$99.46	4.645%	$104.0799	$104.08	$104.10	$104.10
Purchase #5	$212.93	5.150%	$223.8959	$223.90	$223.90	$223.90
Purchase #6	$107.99	11.594%	$120.5104	$120.51	$120.50	$120.50
Purchase #7	$244.31	12.284%	$274.321	$274.32	$274.30	$274.30
7 purchase totals =	$1,121.27		$1,215.4449	$1,215.45	$1,215.40	$1,215.50