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	$30.43	4.801%	$31.8909	$31.89	$31.90	$31.90
Purchase #2	$176.85	4.612%	$185.0063	$185.01	$185.00	$185.00
Purchase #3	$80.92	9.127%	$88.3056	$88.31	$88.30	$88.30
Purchase #4	$19.46	6.459%	$20.7169	$20.72	$20.70	$20.70
Purchase #5	$47.88	11.205%	$53.245	$53.25	$53.25	$53.20
Purchase #6	$24.61	4.699%	$25.7664	$25.77	$25.75	$25.80
Purchase #7	$237.90	10.236%	$262.2514	$262.25	$262.25	$262.30
7 purchase totals =	$618.05		$667.1825	$667.20	$667.15	$667.20