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	$123.45	6.586%	$131.5804	$131.58	$131.60	$131.60
Purchase #2	$41.34	12.801%	$46.6319	$46.63	$46.65	$46.60
Purchase #3	$20.35	7.110%	$21.7969	$21.80	$21.80	$21.80
Purchase #4	$174.72	6.636%	$186.3144	$186.31	$186.30	$186.30
Purchase #5	$169.65	8.754%	$184.5012	$184.50	$184.50	$184.50
Purchase #6	$50.57	8.415%	$54.8255	$54.83	$54.85	$54.80
Purchase #7	$232.55	5.527%	$245.403	$245.40	$245.40	$245.40
7 purchase totals =	$812.63		$871.0533	$871.05	$871.10	$871.00