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	$103.31	7.798%	$111.3661	$111.37	$111.35	$111.40
Purchase #2	$89.41	11.626%	$99.8048	$99.80	$99.80	$99.80
Purchase #3	$124.52	6.179%	$132.2141	$132.21	$132.20	$132.20
Purchase #4	$139.67	10.751%	$154.6859	$154.69	$154.70	$154.70
Purchase #5	$123.31	5.789%	$130.4484	$130.45	$130.45	$130.40
Purchase #6	$71.98	11.329%	$80.1346	$80.13	$80.15	$80.10
Purchase #7	$103.48	10.737%	$114.5906	$114.59	$114.60	$114.60
7 purchase totals =	$755.68		$823.2445	$823.24	$823.25	$823.20