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	$76.29	5.320%	$80.3486	$80.35	$80.35	$80.30
Purchase #2	$108.95	7.347%	$116.9546	$116.95	$116.95	$117.00
Purchase #3	$232.96	9.826%	$255.8506	$255.85	$255.85	$255.90
Purchase #4	$112.82	9.810%	$123.8876	$123.89	$123.90	$123.90
Purchase #5	$51.49	3.153%	$53.1135	$53.11	$53.10	$53.10
Purchase #6	$174.86	6.240%	$185.7713	$185.77	$185.75	$185.80
Purchase #7	$245.26	13.249%	$277.7545	$277.75	$277.75	$277.80
7 purchase totals =	$1,002.63		$1,093.6807	$1,093.67	$1,093.65	$1,093.80