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	$42.39	7.445%	$45.5459	$45.55	$45.55	$45.50
Purchase #2	$228.35	11.755%	$255.1925	$255.19	$255.20	$255.20
Purchase #3	$92.42	11.725%	$103.2562	$103.26	$103.25	$103.30
Purchase #4	$101.46	11.267%	$112.8915	$112.89	$112.90	$112.90
Purchase #5	$228.87	4.255%	$238.6084	$238.61	$238.60	$238.60
Purchase #6	$185.55	9.185%	$202.5928	$202.59	$202.60	$202.60
Purchase #7	$161.92	12.554%	$182.2474	$182.25	$182.25	$182.20
7 purchase totals =	$1,040.96		$1,140.3347	$1,140.34	$1,140.35	$1,140.30