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	$118.80	4.202%	$123.792	$123.79	$123.80	$123.80
Purchase #2	$250.34	10.660%	$277.0262	$277.03	$277.05	$277.00
Purchase #3	$182.31	10.731%	$201.8737	$201.87	$201.85	$201.90
Purchase #4	$129.61	11.113%	$144.0136	$144.01	$144.00	$144.00
Purchase #5	$114.68	7.648%	$123.4507	$123.45	$123.45	$123.50
Purchase #6	$77.76	6.129%	$82.5259	$82.53	$82.55	$82.50
Purchase #7	$26.40	5.470%	$27.8441	$27.84	$27.85	$27.80
7 purchase totals =	$899.90		$980.5262	$980.52	$980.55	$980.50