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	$138.97	12.450%	$156.2718	$156.27	$156.25	$156.30
Purchase #2	$75.93	8.274%	$82.2124	$82.21	$82.20	$82.20
Purchase #3	$233.89	5.854%	$247.5819	$247.58	$247.60	$247.60
Purchase #4	$152.64	8.577%	$165.7319	$165.73	$165.75	$165.70
Purchase #5	$165.28	4.441%	$172.6201	$172.62	$172.60	$172.60
Purchase #6	$151.41	8.552%	$164.3586	$164.36	$164.35	$164.40
Purchase #7	$194.59	12.822%	$219.5403	$219.54	$219.55	$219.50
7 purchase totals =	$1,112.71		$1,208.3170	$1,208.31	$1,208.30	$1,208.30