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	$32.43	10.372%	$35.7936	$35.79	$35.80	$35.80
Purchase #2	$98.69	13.297%	$111.8128	$111.81	$111.80	$111.80
Purchase #3	$35.70	6.314%	$37.9541	$37.95	$37.95	$38.00
Purchase #4	$97.48	8.126%	$105.4012	$105.40	$105.40	$105.40
Purchase #5	$49.41	9.392%	$54.0506	$54.05	$54.05	$54.10
Purchase #6	$75.45	11.228%	$83.9215	$83.92	$83.90	$83.90
Purchase #7	$145.89	8.860%	$158.8159	$158.82	$158.80	$158.80
7 purchase totals =	$535.05		$587.7497	$587.74	$587.70	$587.80