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	$41.50	3.154%	$42.8089	$42.81	$42.80	$42.80
Purchase #2	$231.35	5.577%	$244.2524	$244.25	$244.25	$244.30
Purchase #3	$50.47	11.738%	$56.3942	$56.39	$56.40	$56.40
Purchase #4	$167.39	3.192%	$172.7331	$172.73	$172.75	$172.70
Purchase #5	$142.27	12.434%	$159.9599	$159.96	$159.95	$160.00
Purchase #6	$207.44	13.131%	$234.6789	$234.68	$234.70	$234.70
Purchase #7	$167.34	13.305%	$189.6046	$189.60	$189.60	$189.60
7 purchase totals =	$1,007.76		$1,100.4320	$1,100.42	$1,100.45	$1,100.50