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	$94.81	5.765%	$100.2758	$100.28	$100.30	$100.30
Purchase #2	$69.57	12.870%	$78.5237	$78.52	$78.50	$78.50
Purchase #3	$75.71	7.526%	$81.4079	$81.41	$81.40	$81.40
Purchase #4	$90.28	4.588%	$94.422	$94.42	$94.40	$94.40
Purchase #5	$36.55	12.426%	$41.0917	$41.09	$41.10	$41.10
Purchase #6	$191.91	8.715%	$208.635	$208.64	$208.65	$208.60
Purchase #7	$220.45	8.182%	$238.4872	$238.49	$238.50	$238.50
7 purchase totals =	$779.28		$842.8433	$842.85	$842.85	$842.80