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	$87.30	13.192%	$98.8166	$98.82	$98.80	$98.80
Purchase #2	$108.87	10.842%	$120.6737	$120.67	$120.65	$120.70
Purchase #3	$44.39	6.209%	$47.1462	$47.15	$47.15	$47.10
Purchase #4	$237.31	7.606%	$255.3598	$255.36	$255.35	$255.40
Purchase #5	$150.64	13.813%	$171.4479	$171.45	$171.45	$171.40
Purchase #6	$141.84	4.595%	$148.3575	$148.36	$148.35	$148.40
Purchase #7	$198.89	8.401%	$215.5987	$215.60	$215.60	$215.60
7 purchase totals =	$969.24		$1,057.4004	$1,057.41	$1,057.35	$1,057.40