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	$7.65	6.429%	$8.1418	$8.14	$8.15	$8.10
Purchase #2	$163.38	9.584%	$179.0383	$179.04	$179.05	$179.00
Purchase #3	$104.32	5.104%	$109.6445	$109.64	$109.65	$109.60
Purchase #4	$73.77	5.145%	$77.5655	$77.57	$77.55	$77.60
Purchase #5	$73.39	12.835%	$82.8096	$82.81	$82.80	$82.80
Purchase #6	$104.95	12.874%	$118.4613	$118.46	$118.45	$118.50
Purchase #7	$191.25	12.847%	$215.8199	$215.82	$215.80	$215.80
7 purchase totals =	$718.71		$791.4809	$791.48	$791.45	$791.40