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	$45.57	8.386%	$49.3915	$49.39	$49.40	$49.40
Purchase #2	$57.59	12.761%	$64.9391	$64.94	$64.95	$64.90
Purchase #3	$142.27	7.230%	$152.5561	$152.56	$152.55	$152.60
Purchase #4	$16.93	8.221%	$18.3218	$18.32	$18.30	$18.30
Purchase #5	$40.80	5.614%	$43.0905	$43.09	$43.10	$43.10
Purchase #6	$246.86	3.358%	$255.1496	$255.15	$255.15	$255.10
Purchase #7	$111.77	10.559%	$123.5718	$123.57	$123.55	$123.60
7 purchase totals =	$661.79		$707.0204	$707.02	$707.00	$707.00