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	$154.58	10.646%	$171.0366	$171.04	$171.05	$171.00
Purchase #2	$70.48	4.119%	$73.3831	$73.38	$73.40	$73.40
Purchase #3	$116.47	13.200%	$131.844	$131.84	$131.85	$131.80
Purchase #4	$11.35	6.409%	$12.0774	$12.08	$12.10	$12.10
Purchase #5	$173.57	3.372%	$179.4228	$179.42	$179.40	$179.40
Purchase #6	$153.60	7.815%	$165.6038	$165.60	$165.60	$165.60
Purchase #7	$40.56	5.790%	$42.9084	$42.91	$42.90	$42.90
7 purchase totals =	$720.61		$776.2761	$776.27	$776.30	$776.20