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	$170.69	6.630%	$182.0067	$182.01	$182.00	$182.00
Purchase #2	$63.51	11.585%	$70.8676	$70.87	$70.85	$70.90
Purchase #3	$111.34	12.522%	$125.282	$125.28	$125.30	$125.30
Purchase #4	$135.46	4.459%	$141.5002	$141.50	$141.50	$141.50
Purchase #5	$112.87	4.234%	$117.6489	$117.65	$117.65	$117.60
Purchase #6	$236.52	7.329%	$253.8546	$253.85	$253.85	$253.90
Purchase #7	$153.46	7.316%	$164.6871	$164.69	$164.70	$164.70
7 purchase totals =	$983.85		$1,055.8471	$1,055.85	$1,055.85	$1,055.90