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	$111.38	4.664%	$116.5748	$116.57	$116.55	$116.60
Purchase #2	$149.78	11.387%	$166.8354	$166.84	$166.85	$166.80
Purchase #3	$130.77	8.247%	$141.5546	$141.55	$141.55	$141.60
Purchase #4	$45.55	9.355%	$49.8112	$49.81	$49.80	$49.80
Purchase #5	$239.88	12.148%	$269.0206	$269.02	$269.00	$269.00
Purchase #6	$38.50	4.737%	$40.3237	$40.32	$40.30	$40.30
Purchase #7	$167.59	7.690%	$180.4777	$180.48	$180.50	$180.50
7 purchase totals =	$883.45		$964.5980	$964.59	$964.55	$964.60