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	$39.97	9.770%	$43.8751	$43.88	$43.90	$43.90
Purchase #2	$191.87	13.820%	$218.3864	$218.39	$218.40	$218.40
Purchase #3	$184.93	13.313%	$209.5497	$209.55	$209.55	$209.50
Purchase #4	$123.64	11.722%	$138.1331	$138.13	$138.15	$138.10
Purchase #5	$114.82	8.347%	$124.404	$124.40	$124.40	$124.40
Purchase #6	$243.90	4.649%	$255.2389	$255.24	$255.25	$255.20
Purchase #7	$60.95	7.379%	$65.4475	$65.45	$65.45	$65.40
7 purchase totals =	$960.08		$1,055.0347	$1,055.04	$1,055.10	$1,054.90