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	$10.47	13.860%	$11.9211	$11.92	$11.90	$11.90
Purchase #2	$231.32	7.405%	$248.4492	$248.45	$248.45	$248.40
Purchase #3	$47.97	7.374%	$51.5073	$51.51	$51.50	$51.50
Purchase #4	$13.93	13.862%	$15.861	$15.86	$15.85	$15.90
Purchase #5	$138.95	12.445%	$156.2423	$156.24	$156.25	$156.20
Purchase #6	$35.75	10.667%	$39.5635	$39.56	$39.55	$39.60
Purchase #7	$73.69	11.428%	$82.1113	$82.11	$82.10	$82.10
7 purchase totals =	$552.08		$605.6557	$605.65	$605.60	$605.60