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	$70.63	3.212%	$72.8986	$72.90	$72.90	$72.90
Purchase #2	$105.86	9.710%	$116.139	$116.14	$116.15	$116.10
Purchase #3	$88.45	3.570%	$91.6077	$91.61	$91.60	$91.60
Purchase #4	$20.67	4.377%	$21.5747	$21.57	$21.55	$21.60
Purchase #5	$178.84	6.111%	$189.7689	$189.77	$189.75	$189.80
Purchase #6	$227.89	13.696%	$259.1018	$259.10	$259.10	$259.10
Purchase #7	$225.91	12.792%	$254.8084	$254.81	$254.80	$254.80
7 purchase totals =	$918.25		$1,005.8991	$1,005.90	$1,005.85	$1,005.90