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	$102.88	10.712%	$113.9005	$113.90	$113.90	$113.90
Purchase #2	$114.88	7.151%	$123.0951	$123.10	$123.10	$123.10
Purchase #3	$205.75	9.678%	$225.6625	$225.66	$225.65	$225.70
Purchase #4	$191.27	11.782%	$213.8054	$213.81	$213.80	$213.80
Purchase #5	$214.71	10.860%	$238.0275	$238.03	$238.05	$238.00
Purchase #6	$244.91	8.430%	$265.5559	$265.56	$265.55	$265.60
Purchase #7	$107.75	3.515%	$111.5374	$111.54	$111.55	$111.50
7 purchase totals =	$1,182.15		$1,291.5843	$1,291.60	$1,291.60	$1,291.60