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	$55.26	7.318%	$59.3039	$59.30	$59.30	$59.30
Purchase #2	$107.80	8.371%	$116.8239	$116.82	$116.80	$116.80
Purchase #3	$144.30	4.613%	$150.9566	$150.96	$150.95	$151.00
Purchase #4	$250.88	6.223%	$266.4923	$266.49	$266.50	$266.50
Purchase #5	$98.57	7.147%	$105.6148	$105.61	$105.60	$105.60
Purchase #6	$187.62	13.836%	$213.5791	$213.58	$213.60	$213.60
Purchase #7	$14.74	3.871%	$15.3106	$15.31	$15.30	$15.30
7 purchase totals =	$859.17		$928.0812	$928.07	$928.05	$928.10