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	$200.25	12.760%	$225.8019	$225.80	$225.80	$225.80
Purchase #2	$94.44	12.635%	$106.3725	$106.37	$106.35	$106.40
Purchase #3	$109.91	4.215%	$114.5427	$114.54	$114.55	$114.50
Purchase #4	$236.49	11.791%	$264.3745	$264.37	$264.35	$264.40
Purchase #5	$120.61	7.351%	$129.476	$129.48	$129.50	$129.50
Purchase #6	$160.61	9.410%	$175.7234	$175.72	$175.70	$175.70
Purchase #7	$210.72	5.634%	$222.592	$222.59	$222.60	$222.60
7 purchase totals =	$1,133.03		$1,238.8830	$1,238.87	$1,238.85	$1,238.90