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	$55.41	4.493%	$57.8996	$57.90	$57.90	$57.90
Purchase #2	$144.25	13.291%	$163.4223	$163.42	$163.40	$163.40
Purchase #3	$152.43	10.511%	$168.4519	$168.45	$168.45	$168.50
Purchase #4	$30.57	5.744%	$32.3259	$32.33	$32.35	$32.30
Purchase #5	$111.95	10.496%	$123.7003	$123.70	$123.70	$123.70
Purchase #6	$97.48	5.754%	$103.089	$103.09	$103.10	$103.10
Purchase #7	$167.91	10.518%	$185.5708	$185.57	$185.55	$185.60
7 purchase totals =	$760.00		$834.4598	$834.46	$834.45	$834.50