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	$51.34	8.740%	$55.8271	$55.83	$55.85	$55.80
Purchase #2	$135.30	9.282%	$147.8585	$147.86	$147.85	$147.90
Purchase #3	$76.25	9.703%	$83.6485	$83.65	$83.65	$83.60
Purchase #4	$206.44	10.413%	$227.9366	$227.94	$227.95	$227.90
Purchase #5	$127.59	13.575%	$144.9103	$144.91	$144.90	$144.90
Purchase #6	$140.78	7.106%	$150.7838	$150.78	$150.80	$150.80
Purchase #7	$231.80	5.587%	$244.7507	$244.75	$244.75	$244.80
7 purchase totals =	$969.50		$1,055.7155	$1,055.72	$1,055.75	$1,055.70