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	$131.31	6.323%	$139.6127	$139.61	$139.60	$139.60
Purchase #2	$108.33	10.251%	$119.4349	$119.43	$119.45	$119.40
Purchase #3	$150.55	12.172%	$168.8749	$168.87	$168.85	$168.90
Purchase #4	$243.85	12.829%	$275.1335	$275.13	$275.15	$275.10
Purchase #5	$111.32	5.766%	$117.7387	$117.74	$117.75	$117.70
Purchase #6	$109.43	12.651%	$123.274	$123.27	$123.25	$123.30
Purchase #7	$163.58	8.628%	$177.6937	$177.69	$177.70	$177.70
7 purchase totals =	$1,018.37		$1,121.7624	$1,121.74	$1,121.75	$1,121.70