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	$170.94	10.158%	$188.3041	$188.30	$188.30	$188.30
Purchase #2	$168.73	4.266%	$175.928	$175.93	$175.95	$175.90
Purchase #3	$36.53	11.705%	$40.8058	$40.81	$40.80	$40.80
Purchase #4	$197.57	12.641%	$222.5448	$222.54	$222.55	$222.50
Purchase #5	$159.73	13.732%	$181.6641	$181.66	$181.65	$181.70
Purchase #6	$136.65	11.252%	$152.0259	$152.03	$152.05	$152.00
Purchase #7	$105.61	11.209%	$117.4478	$117.45	$117.45	$117.40
7 purchase totals =	$975.76		$1,078.7205	$1,078.72	$1,078.75	$1,078.60