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	$109.48	6.756%	$116.8765	$116.88	$116.90	$116.90
Purchase #2	$171.47	10.276%	$189.0903	$189.09	$189.10	$189.10
Purchase #3	$101.32	10.351%	$111.8076	$111.81	$111.80	$111.80
Purchase #4	$248.43	11.586%	$277.2131	$277.21	$277.20	$277.20
Purchase #5	$99.52	11.758%	$111.2216	$111.22	$111.20	$111.20
Purchase #6	$211.56	3.281%	$218.5013	$218.50	$218.50	$218.50
Purchase #7	$38.45	4.511%	$40.1845	$40.18	$40.20	$40.20
7 purchase totals =	$980.23		$1,064.8949	$1,064.89	$1,064.90	$1,064.90