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	$66.68	6.672%	$71.1289	$71.13	$71.15	$71.10
Purchase #2	$91.56	4.569%	$95.7434	$95.74	$95.75	$95.70
Purchase #3	$75.77	9.361%	$82.8628	$82.86	$82.85	$82.90
Purchase #4	$178.97	8.493%	$194.1699	$194.17	$194.15	$194.20
Purchase #5	$141.47	12.193%	$158.7194	$158.72	$158.70	$158.70
Purchase #6	$209.88	6.506%	$223.5348	$223.53	$223.55	$223.50
Purchase #7	$158.38	8.359%	$171.619	$171.62	$171.60	$171.60
7 purchase totals =	$922.71		$997.7782	$997.77	$997.75	$997.70