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	$119.35	13.320%	$135.2474	$135.25	$135.25	$135.20
Purchase #2	$75.71	4.262%	$78.9368	$78.94	$78.95	$78.90
Purchase #3	$239.72	7.845%	$258.526	$258.53	$258.55	$258.50
Purchase #4	$131.55	12.805%	$148.395	$148.40	$148.40	$148.40
Purchase #5	$61.72	5.679%	$65.2251	$65.23	$65.25	$65.20
Purchase #6	$244.89	11.762%	$273.694	$273.69	$273.70	$273.70
Purchase #7	$38.75	13.184%	$43.8588	$43.86	$43.85	$43.90
7 purchase totals =	$911.69		$1,003.8831	$1,003.90	$1,003.95	$1,003.80