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	$43.80	4.631%	$45.8284	$45.83	$45.85	$45.80
Purchase #2	$240.98	6.759%	$257.2678	$257.27	$257.25	$257.30
Purchase #3	$187.39	13.363%	$212.4309	$212.43	$212.45	$212.40
Purchase #4	$49.97	10.608%	$55.2708	$55.27	$55.25	$55.30
Purchase #5	$76.61	3.642%	$79.4001	$79.40	$79.40	$79.40
Purchase #6	$227.89	5.519%	$240.4672	$240.47	$240.45	$240.50
Purchase #7	$177.48	13.187%	$200.8843	$200.88	$200.90	$200.90
7 purchase totals =	$1,004.12		$1,091.5495	$1,091.55	$1,091.55	$1,091.60