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	$78.99	4.445%	$82.5011	$82.50	$82.50	$82.50
Purchase #2	$218.72	13.756%	$248.8071	$248.81	$248.80	$248.80
Purchase #3	$190.75	13.755%	$216.9877	$216.99	$217.00	$217.00
Purchase #4	$173.29	9.641%	$189.9969	$190.00	$190.00	$190.00
Purchase #5	$155.44	6.855%	$166.0954	$166.10	$166.10	$166.10
Purchase #6	$59.85	4.793%	$62.7186	$62.72	$62.70	$62.70
Purchase #7	$99.37	6.282%	$105.6124	$105.61	$105.60	$105.60
7 purchase totals =	$976.41		$1,072.7192	$1,072.73	$1,072.70	$1,072.70