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	$38.77	3.319%	$40.0568	$40.06	$40.05	$40.10
Purchase #2	$213.25	13.448%	$241.9279	$241.93	$241.95	$241.90
Purchase #3	$36.80	7.333%	$39.4985	$39.50	$39.50	$39.50
Purchase #4	$93.60	12.600%	$105.3936	$105.39	$105.40	$105.40
Purchase #5	$224.29	5.803%	$237.3055	$237.31	$237.30	$237.30
Purchase #6	$183.69	12.235%	$206.1645	$206.16	$206.15	$206.20
Purchase #7	$79.27	13.158%	$89.7003	$89.70	$89.70	$89.70
7 purchase totals =	$869.67		$960.0471	$960.05	$960.05	$960.10